running costs maths... lpg vs diesel, v6 vs 2.1td

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deian
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running costs maths... lpg vs diesel, v6 vs 2.1td

Post by deian »

Hi again,

Recently i've come across a treasure that I am gonna buy. It is a S1 V6 24v XM, and I will run it on LPG.

So I want you guys to help me work out the running cost, because it's frying my brain, Please remember these number are average figures, so here goes....

Cost of fuel:
lpg @ 42p (litre)
diesel @ 95 (litre)

Miles per gallon:
xantia 2.1 td does minimum 40mpg
xm v6 does a minimum of 25mpg,

*i understand that lpg is not as efficient as petrol, maybe 10% less efficient, so lets take the xm's mpg down to a bad 20mpg to cover that loss
*and also 10% less power, no big deal

So 'say' lpg goes up to a maximum of 45p a litre, it's still going to be 50% cheaper to buy than diesel. And taking in mind the XM may be twice as uneconomical to run 20mpg vs 40mpg. I am back to square one with a few pounds in mu pocket at the end of the month, on top of that the lpg will make the engine run cleaner and be less harmful to the environment, is it true that lpg is better for your engine?

So assuming I get a good example of an xm that runs reliably and doesn't need too much maintenance in the way of big things like starters, clutches, hydraulic pump, etc etc, and the insurance is quite a bit cheaper than the xantia (yes it really is!!) am I right in thinking in will be cheaper to run (overall after all costs are taken into consideration)? ...Especially on the long runs? I do 12 miles to and 12 miles from work on a B road and you get to do a good speed on the road.

Thanks
James.UK
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Post by James.UK »

I seem to recall reading several comments stating that the XM is a rather unreliable car, and a real pain to work on?.. So you sure it's a good swop?? (Xantia = XM?).
.
James. (Nr M67 East of Manchester).
Dark Blue ZX 1.9D Auto 1994 'L' 5 dr (modified) Aura. 98K miles used daily. Ave mpg 40
Wedgewood Blue 75 CTD auto Connoissaur. 2002. 144k. used daily. ave mpg 40 ish.
KP
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Post by KP »

LPG is a better fuel as its cleaner burning and in theory you can get more power out of it if its setup right and you decat. to be hoenst on an XM thats even last of the line the cat will be nearly gone by now anyway so worth removing.

Ive had it and i worked out that in the 23k since ive had it, its paid itself back and a bit more now. The bigger thing was i worked out i was paying about £250-300 a month for about 6 tanks of Optimax and that covered the loan for the nistall and still left me about 4-5tanks of LPG so now im well into the money saving. The tank is small at noly 36litre capacity but it does 190miles on it on a run and does me well.

See locally where the cheapest place is as there are some about that are much cheaper than the run of the mill ones.

Certainly worth doing in my opinion.
jeremy
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Post by jeremy »

Bet V6 XM won't do 25. Govt fuel consumption figures are urban 14.6, extra urban 32.5, combined 22.4.
jeremy
SteveG

Post by SteveG »

can't really comment directly on Citroens running on LPG but my Discovery is converted and I used to run a diesel one so can give you direct comparisons between those.

The diesel Disco (2.5ltr Tdi) used to cost 9.5p/mile in fuel. This figure is based on 126k miles over a four year period.

The petrol Disco (3.9ltr V8 injection) costs 24p/mile on unleaded :cry: or 10.2p/mile on LPG :D. Figures derived from 85k miles over a 4 year period.

I have also noticed that when running on LPG the engine is smoother and more responsive than when on petrol. If I change to petrol as I go along (when running low on LPG) you can tell the difference straight away. If you allow the LPG level to run too low (pressure drops) the engine is prone to backfiring and this can blow plastic intake manifolds/air filter boxes apart. Unless you go for direct injection then some form of backfire protection is a must.
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Post by KP »

I have a system thats fine when it gets low and auto switches over to petrol if it detects lean running as well.

TBH im sure the the V6 doesnt have much in the way of plastic or damagable bits incase of blowback so it little to worry about :)
caveman_si
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Post by caveman_si »

Dont forget to look at the long term cost of the car. IF you intend to keep it for any length diesel is probably better.

LPG is only a cheap fuel as the govenment have a very low duty on it. The level can be changed at any time and i remember reading that its due for a review this yr. So it may be worth looking at first beforee deciding. As for environmantally friendly mmmmm not really its a fosssil fuel but its does burn slightly cleaner then diesel.

Personally id go the diesel as it there is always bio diesel and svo to try if you want cheaper fuel and the parts are more pleantyful and no pesky lpg systems to work on.
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genius149
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Post by genius149 »

LPG burns a lot cleaner than other fuels - hence the lower duty, the reduction in Tax (Vehicle excise duty) and the fact Ken Livingstone lets cars powered by it drive through London free of charge.

It also burns a bit hotter (octane rating is 112) so it is worth getting flashlube fitted to help stop the valves burning out (you can get kits from ebay easily enough).

Personally I think the costs are comparable to diesel but the trips to fill up are more frequent as the tank is smaller and the economy (per gallon) is worse.

Useful place for info is here
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KP
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Post by KP »

The problem is you cant get free congestion it has to have been covnerted by the manufacturer or be on the database thing which aint cheap to do.

No reduction in tax either for people who convert after their car was made either im afraid.
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Post by rossnunn »

its amazing isn't it. There's no real ensentive from the government to go for either bio or LPG, yet it supposed to be much better for the enviroment?
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Post by KP »

Bio is much worse when you realise how much the duty is and how much it is initially :twisted: and unless u bother with WVO and all that guff its not really worth it unless u want the extra power it offers.
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Post by f00lzz »

jeremy wrote:Bet V6 XM won't do 25. Govt fuel consumption figures are urban 14.6, extra urban 32.5, combined 22.4.
Agreed.. mine (old 90deg V6) averaged 22.6 mpg over a 3 year period (thats an average over 70,065)
Ian
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Post by Stewart(oily) »

I found that running the BX on 100% biodiesel actually made it less powerful, 30% seems about right to me, as far as LPG goes, it burns clean, engine oil lasts longer, there appears to be a power defecit in smaller engines and MPG suffers in most cases, but it is still a fossil fuel and Gordon Brown is probably watching it.
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Post by KP »

Just to add i used to use Silkolene Pro R oil and when it came to a change i could swear the oil was still fresh as it retained its lovely pink pigment but i also ran colder spark plugs to help the LPG out as well as it burns hotter than petrol its quicker to warm your engine up as well :)
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Post by Peter.N. »

The XM is not a particularly reliable car, but niether are most hydropnumatic Citroens! but it is a superb car to ride in, I am on my fourth now, in ten years and have never found anything with such a comfortable ride, execpt the CX perhaps. A couple of days ago I tried a friends Rover 75 diesel estate, its nice but comes no where the XM for ride quality and space.

My 2.1 td estate averages over 40 mpg and will do 50+ on a long journey but I dont drive hard or all that fast. LPG seems to give better results with big engines, so on the V6 the cost could be similar, but I wonder how long the gas will stay at its present price!
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