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LPG / Autogas - how 'Wonder'-Fuel?


Well, Its a 4x4, and its socially unacceptable, isn't it - well, unless its a battered Series or Defender, sitting in a field with a sheep dog in the back! And, the knockers do have a few valid points - but, Grrrrr - No, sorry, but MY Range Rover was a very considered choice and actually QUITE sensible.

And the main facet that made it a 'sensible' choice was that Jacqui's gas converted - yup, its a 'Gas Guzzler', literally, it guzzles Gas, but liquiditied Petroleum Gas, NOT Gasoline, AKA petrol.

TWO things about LPG:-

One - its about half the price of petrol

Two:- it's about he 'cleanest' transportable fuel we got.

So, my friends, it may be a hugely inefficient contraption, that uses far more fuel than is needed to do any specific job, BUT, the price of the fuel means that I can afford to live with that inefficiency, AND because its a 'clean' fuel, I am responsible for less harmful emissions while doing it, than some-one with something more conventional.

So, having put two fingers up to the PC brigade - lets look at it a bit more closely, because it SOUNDS too god to be true.

Economics of LPG

Right - well, if you were a really really anal retentive enviro-nutcase - you probably wouldn't even be thinking about a big 4x4 or looking at this site, so I'll deal with the 'green' issues later.

What you are probably concerned with, is the fact that petrol is now pushing a pound a litre, and ANYTHING with the frontal area of a barn door and the weight of an elephant, isn't going to be all that easy on the stuff, no matter what kind of transmission it has.

So, the biggest attraction of LPG is going to be the forecourt price, and the savings that that potentially offers.

Now, on the face of it, the stuff is about half the price of petrol, so, on the face of it, either you are going to save half your running costs or you can go twice as far. Except there has to be a catch, doesn't there?

Well, actually - NOT much - there are a few, but it depends, and yes, the devil is always in the detail, so it does warrant some further thought.

First of all, lets have a look at why LPG is so cheap to begin with. The Exchequer

OK - our lovely government, is pretty well funded from the proceeds of North Sea Oil - Sorry Scotland, but you aint going to get your independence - well, not unless you sign away your interests around Aberdeen, any way!

First of all they flog the licences to take the stuff out of the ground, then they put tax on flogging the stuff, that are just laughable - we've ALL heard the quotes that 95p of every 1 you spend at he pumps goes to the government in duty

BP, Shell, Texaco, should all have credits under their name saying 'A division of HM Customs & Extortion' under their logo's - because they actually take more money for the tax man than they do for themselves, and pretty much as much of each of us individuals as the tax man does!

I mean, think about it - average Jo, earns what, 300 a week, pays about 50 in tax and NI - spends 40 a week on fuel, of which 38 is actually MORE tax!

But any way - Like a Land Rover, I guess HM Gov't aint that efficient, don't work very fast, breakdown a lot, and gives us a lot of grief, but occasionally does something that's useful and worth us tolerating it for. ONE of those infrequently useful things it did, was sort of forget the levy on LPG, when it was hiking the duties on Petrol and Diesel

Then when it realised that it had left a bit of a gap, found out about its environmental benefits, looked about at the growing green lobby, and announced, as a PR exercise that it was being green by promoting it's use by keeping the price down.

In actual fact - the revenue generated by LPG sales was so small, because so little of the stuff is used, that hey could have trebled the duty or removed it entirely and not made as much difference to their annual revenue generation from it as putting 0.01p on the price of a litre of petrol!

ANYWAY - that's the main reason its so cheap - it aint got the duty on it petrol has.

There is actually another - and that is that production of the stuff far exceeds the demand. Which sort of demands a quick look at how mineral fuels are made, or at least, what we get by way of mineral fuels from crude oil.

Not least because its a fairly interesting little topic in its own right. Basically, crude oil is a mixture of a whole load of stuff, of which 'fuel' is only one small part. Stuff is distilled to give us a whole range of products which includes what are known as 'Transportable' fuels. Which are the ones we're interested in.

'Transportable' Fuel

I better provide a technical definition here, and that is for what is known as 'Transportable Fuel'. Transportable fuel, is not fuel to power transport, but fuel that can be moved about to where it can be used. Most fuels are to some degree or other transportable - only some are more transportable than others.

For example - coal - it IS transportable, but really only in bulk, and it's more suited to fixed installations where it can be piled into a great heap and shovelled into a furnace. Likewise, natural gas, it's a transportable fuel, but the easiest way to transport it is to pump the stuff into a fixed pipe, and like coal, its most suited to being pumped along pipes to fixed installations where it can be burned in a boiler to do something useful.

Now, old fashioned steam and traction engines ran on coal, so it isn't entirely un-transportable - its just not that convenient. Likewise gas. Camping stoves and porta-cabbin heaters run on gas and they aren't connected to a fixed supply, they run on bottles of the stuff. Which is where I'm getting at - LPG is actually one of the 'border line' transportable fuels'.

Petrol, diesel, paraffin - all low volatility liquids - easily poured straight out of the refinery, where they have been separated from the crude oil base into a big tank and taken to wherever they are going to be used, and again, poured into another tank, and then pumped into another, until they are burned.

LPG, isn't so convenient - the 'Gas' bit is the give away - it has to be stored and transported under pressure, as a liquid, in a closed container. If it isn't - well, it would just blow away in the wind, wouldn't it. This means that it's actually a more expensive fuel to produce and to sell, because it takes a lot more work to handle the stuff.

BUT, it is one of the many products you get from refining crude oil. You want petrol, you have to distil crude oil.

Doesn't really matter whether you want it or not, what you get is a whole host of 'fractions' that include, mineral oil bases, the stuff that goes to make your SEA20/50 engine oil or EP90 gear oil, or even greases  Beneath those you get the heavier 'bases' that are used to make plastics and synthetics, and above them, you get the lighter fractions, like diesel, paraffin, and petrol, and above those, gases, like propane, and methane.

Basically, from your raw material - crude oil, you get a range of 'products' and whether you have a market for them or not, to make one, you got to make the others - you cant take a 50 gallon drum of crude and turn it all into petrol, or all into diesel, or all into polyester - to make one, you HAVE to make the rest.

So; this is where economics come into play.


Now, main demand for petroleum products is Petrol.

Has been for fifty years, will probably continue to be for another fifty. Over the years though, demand for the 'by products' has changed.

Once upon a time, demand for Diesel was pretty low. It was, in my memory at one time actually less available and less expensive than paraffin, and these days paraffin you almost cant get hold of except in bottles! But nowadays demand for diesel is almost as high as for petrol.

So, LPG is one of those 'by products' of petrol production that is of questionable value - ie it only has any if there is any demand for it - demand depends on price, price depends on demand.

And demand was so low in comparison to the quantity produced, at one time, some of the refineries simply pumped the stuff back into their own furnaces to heat he stills, and vented of what they couldn't use.

But, times change, and the enviro-mental lobby wont let companies do such things, and where it might once have been a case of setting a price that simply covered the cost of bottling the stuff to make it more worth while than throwing it away - these days, its a question of setting a price that including the bottling costs means selling it costs them less than paying to throw it away in an enviro-mentally friendly manner.

Looks like them 'Greens' might have done something helpful, after all!

'Environmental Overhead'

So there aren't very many absolutes in this - but the main point is that LPG isn't a 'cheaper' fuel than Petrol, in terms of the energy and effort that goes in to obtaining the stuff, its actually more expensive, because having obtained the stuf it costs more to handle. And that is actually one of the questions that I come back to when it comes to these 'green' issues. Its a thing known as the 'Environmental Overhead', and its only just something that the enviro-lobby have cottoned on to.

Basically, the idea goes something like this; when you undertake an environmentally 'friendly' act, what you have to be conscious of is that the 'overhead' is not more environmentally damaging than the act itself.

The best example of this is the milk bottle. Used to be suggested that the old fashioned glass milk bottle was environmentally friendly, because it was re-used, recycled, time and time again. The cardboard milk carton, on the other hand was not environmentally friendly, because it was only used once, but at least it was organic material and bio-degradable, while the blow moulded polyethylene milk carton was the most environmentally unconscious container, because it was non re-useable, was made from mineral oil, and the only thing you could do with it was bung it in an incinerator or land fill.

Full 'impact' studies however were quite intriguing, showing that the 'overhead' associated with collecting, sorting and sterilising used milk bottles, was actually greater than making new glass bottles, and THAT was less than breaking down the old ones and recycling the raw material! The Cardboard carton actually had the greatest environmental impact, being made from trees, leading to deforestation, and the energy and resources input into making it, and making it sterile and not leak, meant that it used more non renewable resources than any alternative and wasn't actually all that biodegradable at the end of it. Blow moulded plastic bottler, even though it was made new from non renewable resources, actually had the least environmental impact of all. All because of the 'overhead'.

Long term Outlook

So, two things make LPG cheap - the first is obviously the excise relief it enjoys, and the other is that its a by-product of petrol production, for which supply outstrips demand. As long as the petrol companies have to make more than they can sell, they will sell it for whatever price it will fetch that doesn't see their petrol revenues eroded to much by doing so. And our question is over the long term price advantage and how that might change.

If every-one were to switch to LPG, then obviously its forecourt cost couldn't be subsidised by petrol revenue, and petrol would actually become a by-product of LPG production, and the exchequer, loosing his revenue from Petrol sales would have to rethink the excise relief the stuff sees if he wanted to balance his books.

Realistically though, LPG is still in the assurgency. Ie: comparatively, its use is not great, and its unlikely that things will change significantly in the short term - certainly not in the three to six years that most people will keep a car.

So, within realistic boundaries, its probable that LPG will enjoy most of its price advantages, if not all of it, for the foreseeable future, and the risk of uncertainty is probably no greater for LPG than it is with petrol - I mean how many times have we seen petrol prices go up in the last two years, and by how much?

LPG could be similarly effected, and its possible that the excise could be hiked a lot more than it could on petrol or diesel, without the country grinding to a halt in the midst of petrol strikes or fuel riots, but even if it was, it is unlikely that it will loose it's excise relief to such a huge extent as using it was as expensive as petrol. Ie: the price may go up, but then so might the price of petrol - as long as LPG remains cheaper than petrol, you'll still be better off, just not as much better off.

Costs & Savings

Which REALLY is the question. How much better of, would you be, by going gas?

OK, well at the moment, LPG prices vary from between about 39p/l and 46/47p/l depending on where and how you buy it. Petrol and Diesel have now both crept up over the 90p mark.

Round by me, most of the forecourts, until recently were 89p/l Petrol 91p/l Diesel, looking vaguely around recently, and further a field, seems that 90-91p/l is more the norm for petrol, and Diesel somewhere between 91-93p/l. Alarmingly I did see one forecourt pricing its Diesel at 96p/l., and I guess it wont be long before more get up to that dizzy height, but still.

Lets say for the sake of argument, Petrol and Diesel are both 90p/l, and that LPG is 45p/l, ie half the price. This is not a hugely accurate study, but just something to get us in the right ball park.

Now, average person has an annual fuel spend of something like 1200-1600. this is important, I've not said that they do X thousand miles a year, or have cars that do Y MPG - what I've said is that they tend to spend about Z a year on fuel - whatever they drive, however they drive it.

Now, if you want the breakdown, it goes something like this; typical driver has a mid sized saloon car, that does something like about 30mpg on average, and covers about 12000 miles a year. 12000miles at 30 mpg is 400 gallons of fuel, or 1800 or so litres, which @ 90p a litre works out at 1600ish, OK? That's about 135 a month, or 30 a week.

And 30 a week is a convenient figure, because that's about the cost of a fill up.

The 'comfort' zone

Right - now the reason I say this is important, is because the 'costs' and 'savings' equations are completely academic when you put them into the real world, and find that psychology plays a bigger part.

What we find is that psychologically, that weekly 'fill up' is a level of expenditure we are comfortable with. And as long as we are comfortable with it, we 'compensate' to keep our expenditure within that comfort zone. So, if we are feeling a bit impoverished, we'll not use the car so much, or drive it a bit more prudently to keep the fuel cost down. If we are a bit flush, we'll maybe use it a bit more or drive it a bit harder, and not worry too much about the fact that we are actually filling it up once ever five or six days rather than every seven.

It's only when they hike the fuel prices or we come to get a new car, or our circumstances otherwise change, that we pay very much more attention to it, and either recalibrate our comfort zone, and live with the higher costs, or we do something about it, and buy a more economical car.

That said, even then, psychology tends to play its part, and few people trade in their BMW's for Nissan Micras, to save money! Far more common is that they go from a 'sporty' saloon to a diesel estate, and the 'savings' are used not to keep the fuel bill down, but to go more miles.

So - if you get the idea, potential savings going LPG are there, but in all likelihood, you wont see all of it. What is likely, is that you'll simply use the savings to keep your fuel spend within the limits of your own 'comfort zone' and probably use the car more, since your not so worried about the costs. And if you are lucky, you'll keep the fuel bill in the lower end of your own comfort zone and see some useful, if not hugely significant saving

And just to give you the idea, Last year I reckon I did less than 2000 miles, in an 'economical' metro, and I filled the thing up with 25 worth of fuel, about once every six weeks - my fuel spend was what, something like 200.

That car probably did something like 35mpg - and the Range Rover'll probably be lucky to do half that - but even so, that would only lift my annual fuel bill to something like 400 - At that rate it would take me something like eight years to justify a gas conversion kit on what it'll save me in fuel - BUT what it does do, is bring my fuel spend back into the 'comfort zone'

It costs 32 to fill Jacqui's 's tanks from dry - that's about 3 more than filling the metro to the top of the filler spout! Its within the comfort zone, and means that I can run the Rangie like I did the metro, and not be too put out.

When we had Bert, who didn't have gas - to keep in the comfort zone, he didn't get the tank filled, almost ever - he only ever got 30 put in at a time, but doing low miles, it didn't really matter, the running costs overall were not unreasonable, and it didn't justify spending money to convert him.

When the wife started using him to commute in, though, it went from 30 a week being put in his tank, to 30 every three or four days, at which point, it was very tempting to look at fitting a gas kit, and justifying it on the fuel saving.

Which is the first warning, because I've heard far to many pundits applying the simple logic that they spend X a year on fuel, a gas conversion costs Y and since LPG is 50% the cost of petrol, then they will save half X a year, and that will pay for the gas conversion in Z months, but it wont often happen - I'm telling you! It just aint that simple!

Duel Fuel Capability

Lets look at some of the 'catches'; First of all, yes, gas is about half the price of petrol, BUT, when you convert a car to run on gas, its not a complete change over - it can still run on petrol.

And that is important, because what you should be thinking is that this is a petrol car that has the facility to exploit a cheaper fuel, rather than thinking its gas, end of story.

Its Duel Fuel. It can run on either petrol or LPG, how much of a saving depends on how much of the time you can use LPG instead of petrol. If you can only run it on gas for half of the time, then you aren't going to save half your fuel costs, you'll only save a quarter.

Realistically, how much of the time you can run it on gas is pretty variable, but the best you are likely to get away with is perhaps 95%ish, and that's being optimistic.

What you need to realise, is that a car converted to run on LPG is not converted to run exclusively on gas.

The gas kit merely adds the capability to be able to run on LPG - it can still run on petrol, and in fact sometimes, will probably have to.

Most significantly, this will be on start up.

The 'start up' over head

A Duel Fuel car has to start on petrol, not gas, for the simple reason is that the LPG has to be vaporised from its liquid form before it can be sucked into the engine. To vaporise it, you have to get it warm, to get it warm, you have to have some source of heat, and to get some heat, you need to burn some fuel.

So you start the engine and get it up to a temperature where it can start vaporising the LPG, by running it on petrol. Now some engines warm up pretty quickly, others don't.

Rover V8's are not an engine that gets that hot that fast - its a BIG chunk of metal, but it depends on the installation, some of them are better than others - mine can switch to gas with the temp needles on the dash still on the stop, but, it doesn't start running sweetly for a good five minutes after that.

On others vehicles, the warm up time before switchover can be five or ten minutes, though that affliction tends not to be so wide spread these days and really only very old conversions, very cheap conversions or badly installed conversions tend to suffer so badly.

But basically, this means that you are always going to need some petrol in the tank, and you'll have to pay full price for at least some of your fuel.

How much depends on how you use the car. If you do a lot of short journeys, then the warm up time can be quite a significant percentage of the overall use, if you mainly do long runs, then it might be quite insignificant - either way, though, it will still be there.

Next, you can only burn LPG if you have it in the tank. It is not as readily available as petrol, and tracking it down in an unfamiliar area can be difficult. This gives you two considerations; first is how many extra miles you might have to drive to find an LPG outlet, compared to the convenience of filling up at a petrol station on route to wherever you are going. AND, how many miles will you end up doing on regular petrol, when you cant get hold of LPG. Give you an idea, there are some LPG 'rich' areas, and a lot of LPG 'starved' areas.

I live in North Warwickshire, and I have one LPG outlet that is reasonably convenient to my home, that I can fill up at and keep the tanks topped of at when I pass. There are a couple of outlets heading out into south Staffordshire, I know of, and a number heading out into Derbyshire, if I might chance on being able to use if I was heading that way for a laning trip, and there are a number of good outlets in Birmingham, which isn't too far from me, if I'm heading that way. If I go thirty miles to my mother's in Stafford, there isn't anywhere within fifteen miles of where she lives that stocks the stuff.

So, it depends - you will probably track down your localest and most convenient stockists, and use them most of the time, but if your heading further a field, and you top off your tank before you leave, you might be able to get to your destination on gas, but might have to rely on using petrol to get you home.

If, you were say going on a caravanning holiday. I used to build the fuel bill for towing the caravan into the cost of the holiday, rather than my annual running costs. That meant hat before I set out with the van, I had put aside, maybe 200, to fill the tanks before we set off. First job after parking up on site was to go fill up. That done, whatever the cost of the fill up (I had twin tanks on the old Landie, so rarely had to fill up on route, but if you get the principle), that told me how much it cost me to get there. So, I took whatever that cost was out of the 200 and put that to one side - that was our 'getting home money'. We now had a tank of petrol, and whatever was left in the budget to get about while we were away.

Now, presume for a moment, you have filled up on gas to get you to your holiday location, and when you get there, you cant get any gas. You now have to factor in doubling your 'get your home money' and running on petrol for the duration of your stay, which could seriously curtail your holiday activities, or you could end up spending rather a large proportion of your time, running about trying to track down some cheap fuel.

Realistically, the sort of difference it might make may only be a matter of 50 - which in the greater scheme of things is really neither here nor there in terms of your annual running costs, BUT, it could be as much as 200, which while it might still not be too big a proportion of your yearly fuel spend, IS pretty significant if you have to find it in one go, and it comes at a time when you want to spend your hard earned on having a good time, not pouring it down the filler of your damned car!

So, you have to considered both 'best' and 'worst' case scenarios, and not bank on being able to run on gas all the time - if you can, treat it as a bonus, but don't rely on it - give yourself some latitude. How much, really depends on your circumstances - if you are mainly a local driver and don't venture too far from home very often, it might be reasonable to estimate that you'll be able to run on gas maybe 75% of the time. If you do a lot of longer runs into unknown territory, then you might only be able to rely on being able to use gas maybe 50% of the time, perhaps less.

And as we've said, if you can only use half price fuel, half of the time, you'll only see a quarter of the saving.

The 'Power' Loss
Next thing, is efficiency. LPG doesn't release quite the same amount of power as petrol. Difference is only about 5-10%, and really not that noticeable - we rarely use full power any way, so it doesn't make much difference to normal driving, though I sometimes flick the motor over to petrol to get a bit more go and a bit more throttle response if I need to make a tight over take or something.

What you wont notice though, is that to compensate for the lower power output on gas, you'll have the throttle open wider to do the same speed along the same road.

Basically, power = rate of work done, (see:- Motive-Megalomania!) so to do a certain speed down a certain road, requires a certain amount of power - engine will be pulling the same revs, you'll be in the same gear, so if the engine's on gas, to make the same power, the throttle's got to be more open, and dragging in more fuel and air, to make the same amount of power.

Which is a long way round saying, on LPG, becouse you loose 5% power, you'll also loose 5% of your mpg. It's about 1mpg in 20, so if you got 20mpg on petrol, you'd be down to about 19mpg on gas - not a lot, but over the year, it can make a difference.

Real Savings?
Well, in conclusion, the economics of a gas conversion, aren't THAT straight forward, and the imagined savings you might see, being realistic aren't that easily achieved.

Practically, I'd say, no way will you realise the supposed halving of your fuel bill, its just not that straight forward. But, it wouldn't be unreasonable to suggest that you might see a real world saving of something in the order of 30%, give or take depending on circumstances, but how much of that saving will stay in your wallet, and how much of it ends up being spent on more fuel, as you compensate, is pretty much down to how contentious you are. And with a Land Rover - I'd suggest that in all probability, the decision to go LPG, will probably be to get the running costs down to something sensible and within your spending comfort zone, so that running a 'thirsty' 4x4 is actually viable and you don't have to choose something more mundane and sensible. In which case, the cost of the conversion, really ought to be considered in relation to the value or cost of the vehicle, rather in relation to the fuel spend.

And I'll give some idea - fifteen year old Range Rover, with LPG kit, is worth about a grand. Same Range rover without an LPG kit, is worth about 500. Cost of a conversion kit, is roughly 500 - well for a cheap new one or a reasonable second hand one.

Now, buy and convert, and the cost of conversion has not detracted from the value of the vehicle. So its not actually cost you anything to add the LPG kit, it's merely that that value is locked in the resale value of the car. Buy one ready converted, and likewise - cost you more for the car, but it'll be worth more when you come to sell it.

Look at it like that, and think of it as a bonus to be able to use gas, and you'll have a happier life with it, and you'll resent having to put full price petrol in it occasionally, far less, you'll still resent it, but......not as much!

The Environment

Right, well this bit is political. And as an interesting diversion on the topic, if you REALLY want me opinion on the enviro-MENTAL movement, go read the article, "Eco-Rant!" I am not an enviro-mentalist, I am an anti-enviro-mentalist. I'm not anti environment, I think that we do need to consider and respect our environment and the ecology very much - I like this planet - I just don't like a lot of the people who I have to share it with, and particularly the vast majority of socially aware, idiots who have far more enthusiasm for a cause than actual knowledge of it.

So, LPG - basically the stuff is propane. Which, if my memory serves is a simple hydro-carbon with a molecular structure C4H6 or something like that. Basically, nice small simple molecule which can easily be burned completely to give the combustants H20 and C02, or carbon dioxide and water.

Reason this is better than petrol, is that petrol is a very long chain molecule and no two molecules are ever actually identical - lots more carbon in them, and a lot of side groups and additional elements lingering in the chain. This gives a far more 'messy' burn, and instead of going from one compound to two distinct compounds, you get loads of the damn things.

Carbon Mon Oxide in greater proportion to Carbon Di-oxide, then compounds of sulphur, and nitrogen, and often a few heavy metals, but a lot of lower order carbon compounds, or 'unburned' hydrocarbons

Think of it a bit like cotton; toss a ball of cotton wool on tp a fire and because its light and fluffy with plenty of room for air to get around all the individual fibres, it'll frizzle and flare and burn away to nothing pretty quick. Take the same mass of cotton, that's been spun into thread and then woven into a fabric and then screwed into a ball, and what you have is a lot denser, with a lot less room for air to get around the individual fibres, and so it'll burn more slowly, and you'll be left with a lot more ash. Make sense?

So, LPG is about as good for the environment as any fuel can be. the ardent eco-whore will tell you that no fuel is good for the environment, and just because its not as bad as another doesn't mean its OK or any less bad to burn it or even burn more of it - but don't let them annoy you.

Basically, the only thing that they can complain about from you burning LPG, in ANY quantity is that it makes CO2, carbon-di-oxide that is 'suggested', is a greenhouse gas that causes global warming. Which puts me back on the "Eco-Rant!" Which you can read separately, if you are that inclined. Basically, the debate is pretty 'flaky', not saying that there is nothing to it; but in the greater scheme of things, I am not convinced that man-made Co2 emissions are going to lead to the catastrophic disaster that's implied, and even if it is, well, a thousand quids worth of over priced crude burned in a family car each year, is a pretty pathetically small contributor in the whole scheme of things. We need to keep things in perspective, because even if we were to all stop burning fossil fuels tomorrow, global warming would continue, and the rate it would continue, wouldn't change much.

So, on balance, quality of life, and all that, we are not all going to be convinced to return to a hunter-gather existence living in 'simple' harmony with the environment, so its a question of balancing how we live against the impact that that has. And, in that equation, LPG comes out pretty damn well. Yes, it still puts C02 into the air, but then it doesn't put much else out besides.

And its also pretty easy on your engine too. Basically, the clean burn it has means that you don't get the carbon build up inside the engine - which means that threes less wear and tear - and the burn itself is a bit softer, which is why it doesn't give as much power - but at the same time, it is a bit easier on bearings the transmission. One thing it doesn't have though is lead - and where the carbon deposits from petrol to some degree offer a bit of lubrication like lead did, that's not there either with LPG - so its swings and roundabouts - and for engine life, running it on a bit of petrol now and again is quite good for it.

If it's so wonderful, why isn't every-one on LPG?

OK, good question. I dont know, is probably the short answer. Apathy, perhaps. More likely ignorance. LPG has been around for YEARS, there's nothing new in the technology, or at least particularly new. Its not like its some great breakthrough that has yet to hit the high street; LPG kits and conversions have been around since the 1970's; just seems that they haven't really caught on.

One of the biggest reasons is probably the availability issue, and people have been cautious to spend a lot of money on a conversion kit for a fuel that they cant be sure to get hold of. And I suppose some of it is the 'lore' that the stuff causes poor running, and mechanical problems, but I suspect that the 'main' reason, is probably that for most people, the savings and benefits aren't that huge, or quickly recouped.

The people that have tended to use Autogas, have been fleet operators and high mile drivers, like taxi drivers, or commercial travellers. Basically, for the 'average Joe', going back to that idea of the 'comfort zone' when it comes to filling up at he pumps, as long as they are in their comfort zone, then the idea of spending a large chunk of money on a conversion kit, just to save a the cost of a couple of pints at the local on a Friday night, probably isn't all that appealing.

And there's been something of a 'dodgy' association with the stuff. I mean, round by us, the Local Trading Standard Agency have been working hard to clamp down on 'cowboy' LPG installations, and particularly the supposedly 'professional' installers that fit them. Actually, the reason is not so much that the cars are dangerous, but...... Well, there's a lot of Asian mini-cab drivers, and they have LPG kits fitted, but instead of running on Autogas, they have been using bottled propane or trans-pumped heating propane, and avoiding the road fuel excise altogether. Plus the cars they use are often 'twinned' or 'ringed' so that they have two or three identical cars, all with the same number plates and private hire licence displayed, working in separate quarters of the city........

However, yes, the technology is in the back streets rather than the high streets, and it does suffer an image problem, but that doesn't mean that its all bad. And I think that it's going to start changing in the very near future.

Until a while ago, if you had a car under two years old, and were the first owner, you could get a grant towards the cost of conversion, but that's dried up now, as it wasn't a particularly good scheme. Now, if you have a new or nearly new car, the Road Fund Excise system (tax disk, to you and me) has been altered away from the standard capacity based tariff to one based on polluting potential. Cars with the lowest emission figures pay the least tax, those with the highest, the most. LPG cars, with thier lowest of all emissions, pay the least - by a LONG margin. Only bug-bear of that system is that there's no incentive or discount for older cars converted to LPG, so my 1991 Rangie costs as much if not more to tax that a new Jaguar, running on petrol!

But, in London, that wonderful idea 'the congestion charge' is yet another factor making LPG even more appealing, as they are except. Ridiculous system to my mind; you get charged to take a Nissan Micra into the city, because it takes up too much space, but a Land Rover with twelve seats, is except, because its deemed to be a bus!?! Similarly, a 2CV is charged, because running on petrol, it makes too much pollution. A4l 'Duel Fuel' Mercedes, however, because it has the capability (even though it might not be using it) is except! Crass, but then when was legislation ever 'logical'.

Any way, I think, that those couple of incentives, combined with the fact hat the major manufacturers are looking more seriously at offering 'Duel Fuel' models in the show rooms, plus better and importantly cheaper conversions being available, will start to make it a bit more popular, and hopefully see better and wider availability of the stuff. Disappointing, but BP, at one point promised to have Autogas at all of its franchise petrol stations by the millennium. If they had followed that through, I think we'd have seen the other chains follow, but unfortunately, the petrol crisis hit and they withdrew the pledge.

How does it work?

OK, well, you cant just pour Liquid petroleum gas into your petrol tank instead of petrol, it doesn't work like that, unfortunately. So lets start by looking at how petrol works. Petrol is normally a liquid. Stored in a tank, it's pumped from the tank to the engine, where a carburettor or fuel injector atomises it, and 'meters' it into the airstreams going into the engine.

I'd better explain the term 'atomises'. Basically, the petrol is turned into a fine spray or mist of liquid droplets, that are mixed into the air. It's not 'evaporated' or 'boiled' into a gas, its just turned into lots or very tiny rain drops.

Now, our LPG is a liquidified gas. To make it a liquid, its put under pressure. Under pressure its temperature goes up, so its also cooled. Because its under pressure, we don't need to pump it from the tank to the engine, it can find its way there under its own pressure, but, it will do so as a liquid. To burn it, unlike petrol, that for our purposes burns as a liquid, we need to turn the liquidified gas, back into a gas, and to do that we need to take the pressure of and put the heat we took out when we compressed it back in.

Taking the pressure off, on its own, due to a curious phenomenon known as 'boundary effects' in the science of thermodynamics, will simply result in us getting a 'frost' of LPG, ie it will turn into a solid, not a gas, so to make it 'boil' we have to heat it as well as take the pressure of. This is done in a device called a 'vaporiser'; basically a chamber in which its allowed to expand, whist its heated.

Conveniently, most engines make more Kw of waste heat than they do motive power, so we have plenty of it around to use to do the job, and normally, the chamber or vaporiser is plumbed into the cooling system so it gets hot water from the engine to warm the gas.

This is probably one of the advances in recent years that have seen LPG systems become more 'useful', because in early systems, the gas was often vaporised merely by routing the plumbing close to the hot exhaust manifold, which meant that while it got warm quick, it wasn't very stable! Any way; modern systems will use a vaporiser, to turn the liguidified gas into a 'real' gas, before its mixed with air to be burned in the engine.

Here lies our next bit of equipment, the 'mixer'. This is basically a nozzle that allows the gas to be introduced to the air stream going into the engine, doing pretty much the same thing that the carburettor or fuel injector did for petrol. Only thing is, where you need to mix about a pin head sized drop of fuel in a coffee cup sized amount of air, LPG in the gaseous state is a lot less dense and you need to mix about 20% gas with 80% air.

In other words, its handling a lot bigger volume of the stuff.

This is no great problem, and actually has a couple of advantages. First of them is that the 'metering' or how well the ratio of fuel to air is controlled, isn't quite so critical, is quite a lot easier to set up, but unfortunately is a bit more difficult to vary quickly and easily.

With a petrol system, fuel is pumped into a float bowl, where by the 'pitot' effect, its drawn up a small tube into the air stream blowing across the top.

Metering, can then be effected in a number of ways, but the conventional one was to put a slide into the carburettor to control the air flowing in, with a tapered needle underneath it restricting the flow of fuel out of the pitot tube or 'main jet'. Now, with a gas system, the 'throttle' control from the regular petrol system tends to be retained, but that sort of 'metering' isn't viable. In a typical system the mixer will have something like twenty or thirty 'jets' to mix the fuel and air, and the speed it comes out means that 'choking' the supply would not be feasible.

However, since the metering isn't THAT critical at the sort of typical fuel / air ratio's, and if the basic mixture is about right, older systems didn't bother with any sort of metering adjustment. The only time it needs to be enriched or weakened, is when you accelerate, when a bit of enrichment is helpful, or when you throttle off, when leaning it out is good for economy. AND, because of the burn properties of LPG, the ignition needs to be retarded quite a long way to use it - so its a bit like running on really low grade 'one star' petrol, or having a very 'detuned' engine; in which case, it wasn't THAT much of an impediment, but it did make the car a bit unresponsive. More modern systems, use pressure compensation valves to give a little metering variation, to make them a bit more responsive, though still nowhere near as lively as a conventional petrol engines, and the latest systems, use an electronic manifold injector instead of a 'mixer' which are better still.

Any way, that's the basics of how it works, the important detail bits are that, the gas fuelling system has to be fitted in conjunction with the original petrol fuelling system, so you have two independent fuelling systems, in order that you can start and run on petrol, and then 'switch' to gas if you want it, once the engines warmed up.

This gives a few more complications, where by the 'switch-over' has to isolate each system, and ensure that any residual vaporised fuel is burned off before petrol is added and any petrol in the system is burned off before gas is added, and that you get a 'clean' switch over without the engine going 'lean' and running out of fuel altogether between switch overs. To do this, there's usually some valve control blocks on the fuel lines and gas lines, an in the case of fuel injected engines, often something to turn off the fuel injectors.

And the last thing is the ignition, which has to have different timing of the ignition sparks for gas to petrol, so somewhere there is usually an ignition module that retimes the ignition. Again, with fuel injected engines, the ignition is often controlled by the same 'brain' as the fuel injectors, so sometimes this is combined.

Somewhere, you have to have tanks to hold your LPG and Petrol, fuel gauges for both, a switch or tap to change between fuels, and maybe a warning lamp so you can see which you are running on. And that's about it!

So What's it like?

Right, well, first of all, that 5-10% power drop we mentioned FEELS like a lot more, because as I said, the set up requires the ignition retarding a long way, and the fuel metering isn't so brilliant, so the engine is a lot less responsive. And I make the differentiation, because its not THAT much less powerful, its just that responsiveness is the ability to give you the power when you need it. On LPG, the power is there, just it's a bit tardy in delivering it.

I find that if I am contemplating having to make a swift over take or find a gap pulling out of a junction, I'll often anticipate it and switch to petrol, just to give me that bit extra zip for the manoeuvre, and switch back after, but that's a bonus really, most of the time it's not at all noticeable, and really the performance is not THAT dulled by running on gas.

At least in a big heavy Range Rover with a lazy four litre V8 in it.

I bumped into a chap at he petrol station the other day with one of those little 'midi-vans' - I commented that I didn't think that they used enough petrol to justify going to LPG, but he explained that it was down to the gaffers and the tax advantages.

What he did say though was that the one he had was a 1300, where the old ones they had were 1000cc, and he reckoned that even though the gas powered vehicles had engines 30% bigger, they still felt 'gutless', and the little 1000cc vans felt a lot more lively, even fully loaded.

Which kind of bears out my impressions; its not 'maximum' power, that's important, but 'useable' power, and here, LPG's deficit is a LOT bigger than the 5% that the Dyno suggests.

So, I suppose, it depends on the installation, but if going gas, the bigger the better, I reckon.

Next, warm up is crucial, and most systems tend to be a bit eager to switch over to gas, which I don't think is all that useful. But it's one of those things, people judge the conversion by the 'warm up time'. Plus, most people don't warm their engines before driving, they get in, switch on, into gear, and they are off. In the old days when cars had chokes, warm up discipline was a little better enforced, but these days our standards are different, but taking a few moments to let the engine warm is still a good idea, and especially so on gas. Systems that auto switch will tend to switch when the throttle is blipped, so again, this can make the change over even earlier.

On my system, I've not really noticed any great problem with rapid to gas change-over, except in the recent cold weather, when pulling away, and for the first five minutes or so, I have noticed the engine note was been quite different and its been a bit reluctant to pull, and I suspect, possibly missing the odd firing. Solution was fairly simple though; I have simply turned the engine on before I have tried stowing the steering crook lock or putting my seat belt on, to give the motor an extra minute or so to warm, and then I have left it switched to petrol until the temperature needle has actually moved off the stop, and changed manually, rather than leaving it to 'auto' change.

And to be honest, this is probably a good idea, any way. I pretty much have been able to run on 99% gas, only using petrol for start up, because I've not been cough unable to get gas when I needed it. However, if you do run mainly on gas, then chances are you will wont keep the petrol tank filled up, which will mean that over time, condensation will collect at the bottom of the tank, contaminating the fuel. Plus if you don't use the petrol in the fuel tank in a reasonable period of time it will go 'stale'.

So its good discipline to use a bit of petrol now and again to flush the system through and keep it in good order, and I reckon I might as well do that by making sure the engines well warmed to avoid gas troubles, as by anything else. And remember that bit about gas not having lead or leaving carbon deposits? So reckon its worth while, not being 'over' keen to run on gas ALL the time, and take the trouble to warm it properly on petrol.

Filling up?

Daunting the first time, you soon get used to it. Basically, you have a bayonet coupling with a pressure valve in it, for your filler, and the nozzle on the pump twist fits to it. You then pull the trigger on te hose and lock it open, the go to the pump, press a button, and hold it pressed either until you have put in your desired quantity or the thing cuts out or stops pumping when the tanks are completely full.

And apart from the grin on your face and the slight patient expression as you take twice as long as any-one else to put half as many quids worth of juice in, that's about it. Just remember to put a bit of petrol in from time to time as well!

Finding the stuff, I've mentioned, it can be patchy, but you'll soon start looking out for Autogas stations, and stopping to top the tanks when you have the opportunity, rather than when you are running really low.

You'll then discover Murphey's law works in strict abeyance, as as ten minutes after you've topped the tanks, you'll pass another station selling Autogas 3p a litre cheaper - but hey - you've already saved 40+p a litre to buying petrol, so don't grumble!


Worthy of note; When I started looking for Jacqui, I was forewarned that I should walk away from anything that didn't have a certified installation, otherwise I'd find it impossible to insure. Well, Jacqui didn't have a certificate, but at the price, I couldn't walk away. and what I discovered surprised me.

I had a bit of a nightmare getting insurance, but it was nothing to do with the gas conversion, it was because of the intent to put a seven seat kit in, my 'change' in domestic circumstances, and the fact that I was buying a new car because the old one got nicked!

Any way, out of twenty or so 'high street' insurance companies, only ONE even asked if I had an installation certificate, and when I told them, 'no' they told me that if I took it to my local garage and got them to look at it and write a letter saying they'd checked it was safe, then that would suffice.

Most, did go and check with their underwriters, but apart from asking me if it was a 'professional' installation, none of them seemed particularly bothered about it, or considered it a modification that would effect the premium.

It's worth looking into, because Insurance companies are a cantankerous lot, and will give different answers to the same question to different people on different days; BUT, it seemed that for the most part, that they have a greater understanding and tolerance of the fuel these days. Which, again, bodes well for the future.

Conclusion Well, end of the day, I REALLY cant see too many draw backs with this stuff, and have to say that its lived up to its promises. Having taken everything I'd read with a pinch of salt, and worried over the performance loss, and possible mechanical nightmares of ignition and fuelling hassles, not being able to find an Autogas outlet and all that stuff - No, MY experience has been very positive. I expected a few 'niggles' and I was cautious as to the savings I could realistically expect. End of the day though, I've been able to run on gas FAR more than I anticipated, which I'm treating as a bonus.

First few days, running on LPG, I was reasonably impressed and not at all disappointed with the performance. It was only when I switched it over to Petrol, that I noticed just how big the power gap is, in real world driving. But again, I thought about it and rationalised it that it wasn't 'lost' performance on gas, it was 'added performance' on petrol. I mean, while the difference is pretty Jekyll and Hyde, if I'd gone Diesel, the performance wouldn't be even as good as the V8 on gas, and there would be no 'magic' button to give the thing a boost if you wanted it!

And that I think is probably about it. If you want a V8, because you want power, then you might be a bit disappointed with how LPG blunts it, but if you are interested in economy? Well, its cheaper to run than my Metro, which was cheaper to run than my motorbike! AND the thing still has 'adequate' performance.

So, if this has stimulated your interest in the topic; well, I may have to create something more technical for the 'theory' section, at some point, but for now, I have dug out a couple of articles for you to consider. One is a 'second opinion of an LPG conversion, the other on a home LPG installation on a 3.9 V8, in fact the conversion Jacqui's got, I think!.

V-Cheap V8


I crated this article in the spring of 2006, and since then fuel prices have been going CRAZY! Diesel not only hit a pound a litre, it has, in some places beaten 1.10! But it has been fluctuating a bit, depending on how much coverage Bush has been getting on CNN!

Any way, LPG Prices have crept up, and its now typically about 51-52p/l, but if you hunt about you can find it down in the mid 40's. Some retailers have been a bit sharp, and when thy have re-priced their petrol & diesel, they have added as many pence to a litre of LPG as they have to the DERV! Others, and I WILL mention amongst them, 'Morrisons' supermarkets, who probably have the best national coverage with LPG on MOST of their forecourts, have 'Split the Difference' and maintained the price ratio, which actually makes the savings on LPG slightly more favourable.

Which POSSIBLY explains why there seem to be a lot more people in the queues for the LPG pump at the stations now! Two years ago, there was rarely many people waiting for LPG, and when you came across other people filling up with the stuff, they tended to b vans, taxi's or other Range Rovers! Now, the queues are longer, and people with Ford Focus's and the like are running on it! Maybe it's 'catching on'!

Only other thing to add, is that since creating this, I have expanded my offerings on the topic of 'economy', and you may now also be interested in:-

Eco-Drive - A look at the economics of motoring and getting the most travel for your money

Fuel Frugality- An Answer to the FAQ How Do I get Better MPG.


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