double or not ???

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double or not ???

#1 Post by grahama » Sun Aug 30, 2009 9:16 am

Hi all,

I am debating a petrol A6 which does a quoted 35ish mpg. Will the use of an LPG conversion keep the mpg the same or is some lost with LPG use?

My aim is, (with the half price of lpg), to double the miles attained from the same fuel cost outlay. Hope you got me !!!



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#2 Post by Gilbertd » Sun Aug 30, 2009 10:52 am

You tend to find that you'll use slightly more, how much will depend on whether you do a lot of motorway miles or town work and the type of LPG system fitted. I understand that older mixer systems are good on long runs but tend to be less good around town with modern injection systems the other way round (but don't quote me on it!). If a car will do 35 mpg on petrol I would expect to get around 30 ish on LPG. The equivalent mileage depends on how much you pay for gas as the prices varies far more than petrol.

My car for example will do around 30 mpg on a run on petrol and on the equivalent run on gas, I'll do something like 240 miles on a 46 litre fill so that's about 24 mpg. Assuming petrol at 103p a litre (which it was the last time I looked) and gas from my local BP station at 52.9p per litre, that'll give me the equivalent costs on gas of about 47 mpg. However, I don't fill up at the local BP unless I can help it, I fill up at the local Flogas depot at 44p per litre which gives me an equivalent running cost to 54 mpg on petrol. I would think most systems would do better than this as I'm talking about a 13 year old Saab 900 with 243,000 miles on the clock fitted with a 9 year old single mixer LPG system.

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#3 Post by Active_Lad » Sun Aug 30, 2009 5:08 pm

As a rough rule of thumb on a mixture of town and long distance running, you will use 15-20% more fuel due to the difference in calorific values between Petrol and LPG but the fuel is about half the price. So, you will save about 30% overall. Therefore, if you're spending £1000/Yr on Petrol now, you'll spend about £700/Yr on LPG.

Your conversion costs will depend on the system and whether you do a DIY install or get it fitted professionally, so any savings you make in the early years will only offset the capital cost of the conversion. Again, as a rough rule of thumb, it will take about 40,000 miles to recoup the costs of a professionally installed system, less if you go the DIY route.

Your actual payback will depend on the system installed, the car itself, the driver and the sort of driving you do, so there's no quick and easy answer. It will hurt when you write out the big cheque at the beginning for the installation, but you'll smile every time after that when you fill up at the pump! :lol:

One thing to check is the price of LPG in your local area or in places where you fill up regularly as that will also determine the payback period.
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#4 Post by johnnyboy » Sat Oct 03, 2009 9:16 am

I've not sat down and worked it out but for 85 litres of lpg my 4.0l Range Rover returns just under 300 miles I am more than happy with that :D

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