MPG-going down

[kentishvanman]

Hi
Anyone got any bright ideas about where my fuel is going.
Vehicle is E reg Auto sleeper 1.9 DG (auto box) high top. 85,500 on the clock. LPG converted.
I used to get around 27mpg on petrol the last time I checked about 6/7 years ago.
Have been running on gas since 2008 when I got 23 mpg but the the last set of figures (based on 1700 miles)gave me 13/14 mpg. Motorway/town/rural driving.
The van was checked/adjusted (lpg) just before last trip.Mpg has steadily got worse, it has not happened suddenly.
It runs fine. It cruises along at 55/60mph on motorways, slow up the hills, arn't we all, starts fine, sounds fine.
Plugs are the right colour in fact no complaints except the amount of gas I'm putting in. I know it's cheaper than petrol but that's not the point.
I am going to spray gas detection fluid around tomorrow to see if there is a leak anywhere but don't know what else to do.
All input welcomed.
Don

[HarryMann]

I used to get around 27mpg on petrol the last time I checked about 6/7 years ago.
Have been running on gas since 2008 when I got 23 mpg

Honest answer???

They are far too high initially... you'd need a Subaru 2.0 or 2.2 to be getting 27 genuine from one of those campers IMHO

and check your air filter(s) and tyre pressures

This is the clue...

I used to get around 27mpg on petrol the last time I checked about 6/7 years ago.

Spot checking fuel consumption serves little purpose, other than misleading you or others; running a proper tab over a few thousand miles is about the only way of creating a line in the sand you can refer back to with any confidence.

[kentishvanman]

Hi,
Thanks for reply.
I've had my van since 1999 and I checked the fuel consumption from day one. The last check that I mentioned was the final result done over a 2500 trip around Scotland. When that result was compared/included in the previous 5 years computations the result was 27.12 mpg. After that I stopped checking regularly but the odd spot check gave the same results.
When I got 'gassed up' I started checking again and initially had 23.77 mpg but this has been decreasing to the present 13.85 mpg. and I think there must be a reason.
There have been posts where members say they achieve around 27mpg and other posts where the consumption is around 13mpg. The latter figure usually brings responses that this is a bit on the low side.
Air filter cleaned/changed regularly as is oil, plugs etc. Tyre pressure maintained as handbook suggests, from memory 37psi (front) 49psi (rear)
So I think there must be something 'wrong' somewhere.
Don

[BOXY]

If you can't find any gas leaks, and the engine / ignition seems to be set-up and running correctly the only other suggestion I can make is an increase in the rolling resistance. If the tyre pressures are right maybe a brake is starting to drag?

[HarryMann]

OK then, we'll take thos figures as gospel (even though VW would have been delighted with them I feel)

Have you changed your method of checking the consumption ?

Is your (petrol) tank leaking?

Even if you aren't checking the consumption, something that drops by about half would have been noticeable surely... ? So approx when did this happen and what changed if anything a round that time.

{Sorry, but I get the feeling we're going to have lists and lists of things to check and then ...........................................}

Because nothing I know of would halve the fuel consumption that wasn't pretty obvious, (other than methods and sums )

If you weren't saying it was going well - I'd say as always - first check the compressions hot & cold

check carb float chamber/needle valve
and then manifolds for air leaks.

As above all 4 wheels for binding (brakes been done lately)
Gearbox oil (check for weeps around the various box casting joins, not uncommon as they age and corrode, have known total oil loss between services due weeps on T25 boxes)

But you say everything is Ok, starts, idles, runs OK... it can't be if your figurework is correct!

[Cruz]

I jump for joy if my mpg hits 20. it's always 16-17 and has been ever since I started my little book when I got gassed. No trip on my speedo so the book is invaluable for checking if I am near to running out

[HarryMann]

Yes Cruz, quite right, trip is no good for checking mpg, must be continuous mileometer readings and fuellings in the book, with brims marked up.

[kentishvanman]

Hi,
Method of checking always the same ie fill to brim (petrol or gas), read odometer, drive, then repeat.
Petrol tank ok, I run on gas.
Nothing happened suddenly, just mpg started going down.
Ignoring the pre gas days after the conversion I was on 23mpg then it went down to 20mpg then 18/19mpg and the last trip was 14mpg. That averages out at 18+mpg but if all the trips are of a similiar nature then each journey should calculate at about the same. I agree it can't be ok if the figure work (double checked) suggests otherwise but I can't fault the perfomance.
Anyway thanks for the suggestions. Will check out combustion, carb, manifold and brakes although I' m sure they are ok. Gearbox is an auto. Thought maybe the bands in it were loose but there ok.
Have a lot going on at the moment so will take time to do all the checks but will come back with any findings.
Don

[Cruz]

You may need your LPG system adjusting

[kentishvanman]

Hi,

The van was checked/adjusted (lpg) just before last trip.

It runs fine. Can't fault it.
Agree with HarryMann there IS something wrong or the figure work is incorrect.
Will keep looking and checking. I'll find an answer
Don

[lloydy]

If you always use the same place to fill up maybe they need the weights and measures people to check the pump accuracy