Which is cheaper to run LPG or Diesel car

Which is cheaper to run, something like a Skoda Octavia sized diesel or a converted LPG petrol car of similar size? And any other advantages/disadvantages of lpg v diesel? I am talking of annual mileage of 12-15000 miles or so per year.

How do you work out the cost benefits. I am not sure how to rely on the fuel consumption figures, as you get quote 3 figures plus the combined one. But people say that these official figures are pie in the sky figures.

Obviously buying a diesel car saves all the hassle and expense of having to pay for a petrol car to be converted, unless you buy one already converted. It seems buying a secondhand LPG car is a much cheaper option than buying a petrol car and paying for it to be converted.

Why doesn't everybody just buy diesel cars if they so much cheaper to run? I guess the performance of an LPG petrol engine might make an LPG car a better choice for some? But then again a lot of these new diesel cars are supposed to be pretty good, with high MPG for even good sized cars.

Reply to
George
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At best, an LPG conversion will return about 10% fewer miles per litre. More typically it is between 10 - 20% fewer. You can also expect a slight loss of power. All this is because LPG has less energy density than petrol (fewer calories per litre), and is being used in an engine that was designed around petrol.

In terms of daily running expenses, at current prices it is resonable to expect fuel costs to be around 60% of what they are on petrol - this is based on my local 38 - 40 ppl, though there can be significant price variations on LPG in some places

If the running costs are your primary motivation, get some quotes for conversions (probably 1,000 - 1,200 ukp for this size of car) and work out the payback period. If you plan to keep the car for longer than this, it becomes an economic proposition. Also bear in mind that some cars, less than 5(?) years old, may be eligible for grant aid from the Powershift scheme

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Remember, also, that LPG is potentially kinder to both the engine and the environment. Some people like to factor in these considerations.

Check with your insurance company to see if they need an LPGA or engineer's certificate that says the conversion is correctly done. If they do, and you buy secondhand, make sure it either has this, or you can get a converter to inspect it and issue one.

Depends what your objectives are. Money isn't always the bottom line. Maybe a modern diesel is different to the slugs that I've diven in the past. Maybe they're cleaner, too.

Reply to
Stewart Hargrave

I suspect there's not much in it really.

The "fuel consumption" figures are not really that; they're actually mathematical models based on exhaust emissions! No manufacturer ever meters the fuel used per mile. The cars are tested in a wind tunnel on a rolling road and the emissions are what is measured. Crazy but true! Which explains why you rarely achieve the quoted figure.

That is certainly a good route to take, and one that I'm following right now. Last year I changed jobs to one 25 miles from home, and decided I could no longer afford to run my Saab 9000 auto at 25mpg, or the old Merc 230TE auto at 26mpg. I broke the Merc (engine was blown) and sold the Saab and bought a Rover 218SLD in the interim. That returns about

45mpg on my daily run, which is more affordable, but the car is really too small for my needs; when my son has an ice hockey match it is a struggle to get all his kit in the boot and his sticks have to sit between the three kids on the back seat. Bear in mind here that I'm accustomed to luxury-type cars, so it's difficult to find a cheap large diesel, especially in an estate which is my preference. So I found an Omega estate with an lpg conversion (just needs a new engine, see thread elsewhere). My reasoning is that the Omega should do about 25mpg, but the price differential will make it effectively 50mpg. I get a bigger, more luxurious car, which will cost me less to run!

Noise, performance, emissions. I know they're getting better, but they still lag behind petrol models on these counts. I bought the Rover because I've had one before and it was a good car. When you're driving there's little noise to remind you it's a diesel, but then it's top-of-the-range and so has better soundproofing than cheaper models. And it's certainly noisy externally when I start it; I'm sure the neighbours don't appreciate it when I start it up and idle while I scrape the front off the windows at 7am! Performance, yes, it's no slouch, and this can be said of any turbo-diesel. But it does rely heavily on that turbo for performance, so it doesn't pick up too quickly from standing. And the rev range and power band are more limited. My last few petrol-engined cars would accelerate quickly from the lights; while the Rover is not embarrassing it does sometimes get left. Emissions - many diesels now have cats, but they don't stop particulates. They tend to smoke. OK, my Rover is a high-miler (176k), but even though it sailed through its MOT last month, it still chucks out a puff of smoke on hard acceleration, and at a cold start. Any petrol car that does that is knackered.

This is my eighth diesel car, but on balance I prefer petrols to drive. LPG combines the "economy" of a diesel with the refinement and performance of a petrol, while outdoing both of them on emissions.

Reply to
Chris Bolus

I did the figures a while ago for petrol, diesel and LPG volvo S60s.... pasted below. Basically LPG is currently cheaper in fuel cost per mile than Diesel, but only for as long as the chancellor allows its lower taxation. Diesel's advantages are availability and range between fills.

"OK - assuming an 850 mile run averaging half way between published urban and extra urban consumption:

The D5 will do 668 miles on one tank, necessitating a refill. The 2.0T will do 476 miles, also needing a refill. The LPG using both LPG and petrol has a range of 474 miles and will need one refill, but only using the LPG tank would need 3 refills as it's range on LPG only is 275 miles. But fair enough you'd want three stops on that journey anyway. Of course you wouldn't push it too far as LPG may be harder to find in the middle of nowhere (sorry... Scotland)

The big question - fuel cost... Diesel £77 quid, Petrol 99 quid, Bi fuel £77 quid, LPG only 62 quid. Interestingly taking the price of the base "S" models into account that means the diesel takes 33k miles to recoup the purchase cost, the bi-fuel run on both tanks takes 32k miles, the bi-fuel on LPG only 19k miles."

Reply to
Tim S Kemp

[...]

I run a 12 year old Saab 9000 CSE manual, the light pressure turbo contributes to efficiency, hence good economy for this size of car. The car is cheap to own since very little goes wrong. Of course there are tyres and synt oil changes.

Another alternative to diesel are the Variable Valve Timing engines, as in Toyota and others, they show remarkable economy close to diesels.

Reply to
Johannes H Andersen

15000 miles will save you about £50 in fuel between diesel and petrol, and about £650 between petrol and LPG.

If you don't get a grant for the conversion to LPG it would take about 3 years to recoup the costs assuming 15000 miles per year. Also assuming the government doesn't hike the price up too.

It would still take two years even with a grant.

My calculations are based on real world average figures.

I have a spreadhseet to calculate fuel costs, miles per gallon, miles per litre, and costs per fuel.

I can eMail it to you if you want.

Yes, it depends on how long you intend to keep the car, if it's not three years then don't bother.

Actually, according to the spreadsheet I have here, it doesn't have that much advantage. A lot of petrol engines can almost match diesels for MPG now, certainly to within 5-10MPG. Even after 30000 miles the difference is only about £110.

That's about the difference in cost between a couple of service - the Diesel being higher.

Reply to
Andy Hewitt

On or around Sun, 27 Feb 2005 13:50:01 +0000, George enlightened us thusly:

Basically, modern diesels are bloody good.

However...

consider such as the Jag X-type. It's available with the 2-litre Ford diesel (IIRC) in 2-WD spec, which is a very good engine, and probably in that guise it returns quite good fuel figures.

It also comes with a Duratec 3-litre V6 and 4WD. This drinks petrol, by comparison. Run the latter on LPG, you should get almost all the performance and about the same running costs as the diesel, at current prices.

by this logic, I had (still have, but not running ATM) a 2.8 4x4 Sierra, which cost about the same in fuel as a 2.3 diesel would've, but is infinitely more fun to drive :-)

Currently, we (as a household) run a brace of LR discoveries. Mother's is a

300 TDi, 2.5 diesel, and will, on the right bit of road, pull 90+ and in normal running around does about 30 mpg.

Mine is a 3.5 V8, goes about the same speed, accelerates marginally faster (but you'd need to time it to notice the difference) but it makes a lovely noise and does about 13 mpg on LPG, which is about equivalent to 28 mpg for diesel (LPG on the pumps is slightly under half the diesel price) but i get most of my gas in bulk, and so a bit cheaper.

There are downsides, of course. Most notable is tank range - if you habitually go the length of the country, you'll find you need a lot of stops for filing up compared with a typical diesel, most of which have tank ranges in the 400-600 mile bracket.

My disco has a range of about 180 miles on LPG, plus about 120 mile son petrol by way of a reserve. For more initial outlay, I could get enough tank-space for about another 180 miles, for 350-360 total on LPG, which still doesn't compare with 550+ from the diesel one.

Environmentally, there's not a lot to choose either. LPG, properly set up, is a bit better than petrol or diesel, but not a lot. It's a lot better than an old petrol or diesel though, so converting old Range Rovers and the like makes a lot of sense environmentally. Pity they don't offer grants for that... Even my pre-cat 3.5i is quite a lot better on emissions than on petrol.

Reply to
Austin Shackles

On or around Sun, 27 Feb 2005 13:50:01 +0000, George enlightened us thusly:

If you're looking at buying new, there are factpory-converted ones to be had. Dunno what the price differences are.

Reply to
Austin Shackles

I had a 9000s auto, and yes I loved the car - in the six months I had it simply _nothing_ went wrong. But it just does not approach diesels in terms of economy. I could have converted to LPG, but then I would have lost boot space, and the boot was only just big enough as it was (yes I know it's huge, but try getting ice hockey goalie kit in!)

Reply to
Chris Bolus

I have to disagree. This is entirely dependant upon the extent of the modifications completed as part of the LPG conversion, and how highly tuned the engine was on petrol.

If you are talking dual-fuel, the engine will always be significantly worse than optimal for LPG simply to be able to run on petrol. If, however, the engine is modified to operate solely on LPG, the engine can be better optimised for LPG. In the case of older carburetted V8s, for example, it is quite achievable to replace a Rochester, Holley or similar carby with an OHG mixer, change the inlet manifold to eliminate intake heat, fit a cold air intake, increase the compression and regraph the spark curve and achieve a significant increase in power while continuing to comply with the emission standards that the engine was originally built to _and_ get better economy at the same time! In the same model engine, it would be illegal to modify the petrol system to get more performance because it would cease to comply with the emission requirements. :-)

Even Ford managed to get the same power from an 4.0L LPG 6-cyl with a mixer and the same engine with multi-point petrol injection in the AU series Falcons (Australia). The economy is 10% worse at worst - I have an LPG model and have compared it to others with petrol.

If you compare the same technology between petrol and LPG, the LPG will win every time. Compare liquid injection to injection, single point mixer to petrol carby...

LPG has less energy per litre, but more per kg. It also has a higher effective octane rating, and can achieve better efficiency if that octane rating is taken advantage of. It should always be possible to get more power, even if it requires more fuel to do so.

Depends how long you plan on keeping the vehicle. If you're going to hang onto it for more than 5 years, this is definately an issue.

Reply to
athol

Much better to simply buy a 3 year old factory built dedicated LPG model for the same price as the petrol model. :-) Been there, done that.

IOW, the cheaper servicing of the dedicated LPG engine wins hands down. :-)

Reply to
athol

At 3 years old, I got a dedicated LPG model for the same price as the equivalent petrol model. 4 months on, the thing is going great and the depreciation is slower than almost any other 3-yo vehicle that I could have bought for similar money. :-)

Reply to
athol

On or around 28 Feb 2005 04:43:30 GMT, athol enlightened us thusly:

not easy in this country, although I believe someone's importing them from Oz.

most of the ones on sale here are dual-fuel, factory authorised conversions.

and WRT the mods on an engine, while I agree with what you say, the required mods make the conversion quite a bit more expensive, and the pay-off time increases accordingly. You also get an engine that won't run on petrol if you need to, which can be an issue still in the UK due to patchy gas supplies.

Reply to
Austin Shackles

Ok, then.

The guy was asking about a Skoda Octavia, or similar.

But this is an extremely long way from the perameters of the original question. The guy was asking about the adantages of having a standard conversion done to a standard car, not something that would need an R&D budget. Upping the compression alone would preclude this from most people's agenda.

But you'll notice that the OP is in the UK, and isn't considering a vehicle which isn't available here.

AFAIAA, none of the major manufacturers are offering an LPG-only option of any of their cars in the UK. Every duel fuel car (including from the factory) is a conversion.

Are you saying that liquid phase LPG injection is now a practical and readily available option for conversions? I didn't know that.

No, not *always*. Not in a *typical* conversion.

But you may remember that I have previously suggested that the major engine developers ought to be getting their act together about exploiting the burning characteristics of LPG. The potential efficiency of a dedicated LPG engine must be far superior to that of a petrol equivalent.

However, this is waaaaaay beyond most people's idea of a simple conversion. I fear you may not have clarified things for the OP.

Reply to
Stewart Hargrave

You fail to point out that you are in Australia, which has some relevance when posting to uk.* newsgroups.

Meanwhile, back in the real world...er, I mean the UK...I am not aware of any dedicated LPG vehicles available from the major makers. It's disappointing, and maybe somewhat surprising, given the tax break on the fuel.

Reply to
Stewart Hargrave

On or around Mon, 28 Feb 2005 13:32:33 +0000, Stewart Hargrave enlightened us thusly:

Mind, ISTR someone's importing the LPG-only cars from Oz. was quite tempted...

Reply to
Austin Shackles

On or around Mon, 28 Feb 2005 13:32:56 +0000, Stewart Hargrave enlightened us thusly:

not really, the bloody govermnent can't be trusted for 5 minutes, if any manufacturer bothered to do the necessary R&D to make a decnt LPG-only motor, TBG would then reduce the tax breaks so that it'd not sell, or something, feckem.

Reply to
Austin Shackles

Another downside is the damage cause to engines. Honda have recently sent us a bulletin saying they will invalidate the warranty on any engine that has an LPG conversion. I know their engines run very hot internally, and are pretty much on the limit of current technology with their emissions levels. Obviously with engines running so lean the internal temperatures get very high, and there isn't any cooling from LPG.

Reply to
Andy Hewitt

I cant wait to see this one torn apart .. talk about a system of misinformation.

Reply to
atec

Yes, 'tis interesting to note the contrast with Ford and Vauxhall who both offer their own factory dual-fuel versions.

Reply to
Chris Bolus

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