V8 Disco LPG only uses one tank ...

I am the proud new owner of a 1999 V8 Disco ES on LPG. It has two 40l tanks where the fuel tank used to be plus an additional square low capacity (25-30l) petrol tank.

Unfortunately it ran out of LPG on the way home after 170 miles and then only took 38.5l on the re-fill. I am pleased with the 20mpg but less so with the fact it is obviously only using one tank!

I will try to contact the original installers on Monday to see if they have any idea but thought I would raise it here first.

I don't know a thing about LPG but assume there must be some tubing and one or more valves connecting the tanks so assume it is a stuck valve of some sort.

The 'gauge' drops from 4 greens to red in about 60 miles and then does the next 100 on red before it switches. This makes me think the tank the car is using is the one it should empty second?

Any info or advice gratefully received.

Sorry I can't answer your query but a few things you may need to know.

LPG tanks only fill up to about 80% of their volume.
The "gauge" is notoriously unreliable, mine gets more greens as the tanks empty!! When you have solved your filling problem use your trip meter as a guide as to when you will need gas.
Try not to run out of gas as it can cause a back fire which can blow your air filter off if not modified.
Make sure your leads and plugs are in good condition, crossed leads can cause poor performance.

Have a look at LPG Discussion Forum • Index page

tanks should have separate non return valve per tank for filling and also separate isolation valve on each tank.

Is it possible it was serviced and they forgot to switch on second tank?

Each tank will have a solenoid valve on it so check the electrical connections to both of those

Try disconnecting then in turn and find out which tank is not working.

Thanks for the advice. I have just telephoned my local LPG installer/servicing garage. They were extremely helpful and I already think that is where it will receive it's next service!

From the paperwork I have it seems it has 2 X 40L tanks as a water capacity so as alexdon says, not an 80L gas capacity .. more like 60L! Not as much as I had hoped really!

I was told that it fuels from a T section with a non return valve in all the three arms. When the pump strained I should have waited till the numbers stopped, apparently! I will fill it in the next day or so and try out this theory. I will be much relieved if it works.

I also learn that cheapo spark plugs with big electrodes are better for LPG than expensive platinum ones with little electrodes - at the moment it has platinum ones which cost £7 each!

It runs smooth on gas and OK on petrol whilst warm but is a bag of nails for the first mile from cold (on petrol). I was told that the car runs preset values when cold and closed loop from lambda sensors etc when hot. It was suggested that I unplug the battery for 10 minutes before next cold start to let preset values reset. I have checked and the radio code is written in the service book - phew!

I will feed back on the filling and resetting soon.

OK, I used the car till it ran out of LPG (handily less than a mile from Sainsbury's ) and then filled up. I continued to hold the button as the nasty noise started at 38L and it carried on filling at the same speed till 64.7L when the pump cut off. LPG capacity of the tanks is 64L so I am pleased to say it was all noobie error! The noise must be to do with what the various non-return valves are up to.

I now have the problem that it is only doing a measured 12mpg on LPG in gentle(ish) driving! As it is much rougher on petrol, horrible when cold and is not as fast as I thought it would be, I conclude that some part of the system is not right and I reckon it is something shared between both petrol and LPG. As I understand it, the LPG system sort of piggy backs the petrol one so I guess I need to start with getting the codes read on the petrol side.