4.0 v8 lpg mpg

Hi guys anyone give me an idea of what mpg i should be getting computer currently reads 12.5 thought it should be slightly better than this

14-17mpg depending how gentle you are, london stop start 9mpg

LPG MPG is likely to be the same as petrol if not a little less due to the lower calorific content of LPG over petrol...its the price which makes it appear to offer better consumption.
Besides LPG is normally a conversion, so the trip computer or display doesnt know what consumption your getting from the lpg itself...only the petrol. It will appear low because normally you only use petrol on start up when cold. Lpg then kicks in automatically when you go over 2-3000 revs.
so if you were getting 15 mpg with petrol, you'll get about 15 mpg with lpg, but for half the price, which in effect makes the equivalent of about 30 mpg if you were driving petrol
enjoy

smartone said:

LPG MPG is likely to be the same as petrol if not a little less due to the lower calorific content of LPG over petrol...its the price which makes it appear to offer better consumption.
Besides LPG is normally a conversion, so the trip computer or display doesnt know what consumption your getting from the lpg itself...only the petrol. It will appear low because normally you only use petrol on start up when cold. Lpg then kicks in automatically when you go over 2-3000 revs.
so if you were getting 15 mpg with petrol, you'll get about 15 mpg with lpg, but for half the price, which in effect makes the equivalent of about 30 mpg if you were driving petrol
enjoy

Click to expand...

Not being picky but cars use about 15% more LPG then petrol for the reason you said (calorific content ie the energy it contains .... less than petrol). so 12.5 mpg does not look too bad!! Add to that the fact thats it way over half price of petrol these days (round here at least)and the engine probs that seem to come with lpg use (never had any with my Audi 4.2 V8 on LPG but seem common on this forum) plus poor availability down south and it hardly seems worth the bother and thats from an ex LPG user!

My 4.0 lpg reads around 17mpg on the dash computer and thats only on a short 7 mile journey to work, I would expect more than that, does depend on your right foot though.

the only way to asses the situation is to fill the lpg tank and the zero the trip computer, run the lpg completely out and then take a reading from the trip. obviouly you keep the reciept for the tank full and work it back from there.

as with any car the mpg depends on all manner of things and quite inportantly the style of driving(hard or gentle) the type of journeys ( long or short) the excess weight in the car (1 person or 5 plus luggage) then theres things like the tuning/servicing of lpg system. condition of the engine etc etc.

the only thing i do is reset the trip everytime i put gas in then i can work out how many miles i have left. also keep the petrol tank about a quater full. the pump in the tank will still run and its not good practice to run it dry!!

ive worked out on avaerage that it costs me around 60 to 70% of what it would cost me on petrol so a 30/40 percent saving, which means at locally to me £1.135 a litre i pay the equivalent of 81 - 94 pence a litre. which brings me to prices last seen around 2003 (i think)

the main thing with lpg on one of these engines (and these engines in general) is not to mistreat them, look after them and the can last!! i think that goes for any machine tho doesnt it!!

or get top hat liners in and they wont slip!!!

As gavbriggs says, the best way is just to keep an eye on the mileage and work it out by cost. I'm getting about 160 miles to a 70 litre tank, which is about 10-11mpg of gas, but I shld be getting around 240 to a tank (15.5mpg) on a 4.6. The computer gives you the mpg as if it was on petrol but you normally get about 10% less mpg on gas, but the lower price more than cancels that out. It's worth going to a local LPG installer to get it hooked up to a computer and check the settings or see if there's a fault in the system.

carl350i said:

My 4.0 lpg reads around 17mpg on the dash computer and thats only on a short 7 mile journey to work, I would expect more than that, does depend on your right foot though.

Click to expand...

fooking ell the last time my 4.6 got 17mpg it was being towed:doh: usualy it does around 10mpg but thats inner city driving for you

6.8 MPG on LPG is what I get. Goes up to 8.9 that's the best I've got out of it. I have a heavy right foot though.

Around 12mpg for town driving and 16mpg on motorway with a 4.0 D2 is what I get. No trip computer, that's from fill up records I keep with a handy app called road trip on the iPhone.

I have a 1995 4.6 Hse P38.
I bought it in 1999 and had an LPG conversion done straight away.
It is currently doing about 15 mpg on LPG. That's for general use - sometimes local, sometimes long journeys, sometimes towing. It does drop on towing but that's my guide - I fill up with 80 litres when the trip is around 260. (it's a 100 litre tank and they ony filll to 80% capacity - automatic switch off by the pump)
So if LPG is nearly half the price of petrol - it's like getting nearly 30 mpg.

P.S. I did have a fancy tartarini kit fitted originally. Had some problems with it but it turned out it was for a 3.8 litre engine not a 4.6. It was removed and a simple induction IMPCO kit fitted and no problems since.

It starts, runs and stops on LPG. I just switch to petrol once in a while to keep the petrol pump alive and move the fuel in the pipes.

one thing to remember, the petrol pump will always run!! so keep a quater of a tank in it if you can!!!

gavbriggs said:

one thing to remember, the petrol pump will always run!! so keep a quater of a tank in it if you can!!!

Click to expand...

My fuel pump does not run when on LPG. When you switch to LPG a solenoid isolates the fuel pump so that it is not running.

On switching back to petrol it is switched back on.

thats a good idea!!! pretty sure most of em dont switch it off tho!! thats why you get issues with em!!

Ignore the dash. That has nothing to do with your LPG conversion. Your computer wont work with the LPG. It will just stay on whatever the last reading was when you were using petrol.
I have the 4.4 v8 (l322) and a full tank of LPG costing £53 gets me 200 miles. I'll let you work it out