MPG on LPG

I had my 2001 4.0 HSE P38 converted to run on lpg a fornight ago, I was expecting a slight drop in mpg but after filling the lpg tank and running it till empty found I only got 13mpg.
I wasn't expecting amazing results but thus far I am a bit dissapointed.
I drive with a very light right foot and running on petrol always averaged at least 20mpg, it makes me wonder if it was worth the outlay for the lpg system.
What kind of mpg are others on here getting, I'm curious to know

patbhoy said:

I had my 2001 4.0 HSE P38 converted to run on lpg a fornight ago, I was expecting a slight drop in mpg but after filling the lpg tank and running it till empty found I only got 13mpg.
I wasn't expecting amazing results but thus far I am a bit dissapointed.
I drive with a very light right foot and running on petrol always averaged at least 20mpg, it makes me wonder if it was worth the outlay for the lpg system.
What kind of mpg are others on here getting, I'm curious to know

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You cannot fill the tank completely and in some cases at least you cannot completely empty it, so your MPG figure may be misleading if it was a virgin tank that you filled. See what it does when you re-fill, check the volume you put in, reset the trip and see what you get.

Datatek said:

You cannot fill the tank completely and in some cases at least you cannot completely empty it, so your MPG figure may be misleading if it was a virgin tank that you filled. See what it does when you re-fill, check the volume you put in, reset the trip and see what you get.

Click to expand...

I 2nd that
I get around 200 miles out of a 80ltr tank and i am running a 4.6 around town also the person that put your system in sould have said this to you.

Datatek said:

You cannot fill the tank completely and in some cases at least you cannot completely empty it, so your MPG figure may be misleading if it was a virgin tank that you filled. See what it does when you re-fill, check the volume you put in, reset the trip and see what you get.

Click to expand...

It was after I had refilled the tank the 2nd time round that I worked out my mpg and found it to be 13mpg.
So far I have to say I've been unimpressed and wonder if the lpg conversion has been worth the money.
The tank should run out in the next couple of days so I will work out my mpg again, lets hope this time I see an improvement.
(the 2nd refill from empty took 56ltr, the tank is 84ltr so expected to get around 65ltr in but understand it will take less on warm days).

I get about 13 mpg on LPG and about 16 mpg on petrol with a single point system on at 4.6 GEMS. I think I still save money using LPG and use it mostof the time. But, it's true, LPG isn't as attractive as it was, the proportionate price differential with petrol having been reduced in the UK since around 2006 (when LPG could be found for 29.9p/litre - around a 1/3 that of petrol) with a succession of pence per litre duty increases that have impacted the proportional differential significantly.

Im currently at 14.8mpg on gas after an LPG service and Im quite heavy footed away from junctions, sit at 60-70mpg. Seeing around 300 miles to £60 gas @ 64.9p a litre

Im happy with 50 miles for £10. I also run a 3.0 TiD Saab @ 42mpg which is 65 miles for £10 @ 1.41 a litre so its not that bad for a 4.6 V8.

Im not that far from you, Ayr

Still need to fine tune the calibration on mine (diy job), but I get around 16.5mpg on gas with the computer reading about 20mpg...It'll drop to 13.5 if I hoon around.
Got a 95 litre tank in mine, holds about 75 litres and I get around 275 miles on tank.

Think you should take it back to where you had it fitted and ask them to check the calibration.

Could it be the 4 litre has to work a little harder than the 4.6 to lug the car around? Also, type of journey (start / stop vs long run)? Tyre pressures, oil changes etc all take their toll.

My '93 Classic was a 3.9 on LPG (essentially the 4.0 P38 is a 3.9 just rebadged - no displacement change was made IIRC)

And I got 12.5 to 14mpg from it.

The 4.0 does need to be worked harder than the 4.6 so will not be as economical.

A tank can only be filled to 80% of the capacity for safety reasons.

My current 4.4 L322 on gas has a 90L tank with a max fill of 72.8L and I get an average of 15mpg (as shown on my fuelly below)

LPG is 15-20% less efficent than petrol so if you were getting between 17-20mpg on petrol, you'll return 12-15mpg on gas, but it is about half the price.

The L322 is returning at 22p per mile and my previous DSE was returning 26p per mile.

got mine Thursday, drove from Blackburn to Walsall at 60 - 70 all the way and was reading 23.4 on my 4.6 51 plate. been driving round town and stuff and its down to 17.8 - 18.

on mine (90 ltr tank) the most I've ever got in was 75ltr from empty.

After a fill I get about 260 miles (mix of town/motorway & towing the caravan) which, according to my basic maths equates to about 16 mpg

I've just done some calculations on a run to Brighton and back, mostly motorway at 70mph.

I was getting 17.2 mpg from LPG. On similar motorway journeys on petrol I get about 18mpg.

I have been tweaking and tweaking my fuel map for a while now and I'm pretty happy with that. I have a multipoint system DIY installed by me.