Discovery v8 new lpg user

[stbb]

I have just bought a v8 disco with bigas lpg system. The gas leval guage has only ever read up to 3 green leds when full and gone to red after about 160 miles on 2 x40 tanks.Now it goes from 3 green to 2 within 30 miles and into red after 50. It still runs on gas . Will it run untill there is no gas left then swap back to petrol or does it switch back to petrol from led reding from gas tanks? Also any ideas on how to fix this, was told that the guage cound be recalabrated with pc software? The other question is there aperes to be a 8ish gallon petrol tank but the fuel guage does not move much, it goes to almost full when fuel tank if filled but i ran out other day when guage was down to about 4/4. The fuel tank is a square box, not original landrover.Any ideas would be realy helpfull

[SimonHobson]

The gas level lights are a bit vague at the best of times. And it gets worse when you have two tanks - the gauge is fitted to one tank only. In general they empty fairly evenly but this is never guaranteed to be consistent. No amount of software calibration can fix that.

My (limited) experience is that the tanks tend to empty in a specific order. On my Disco, the sill tanks would always empty before the rear tank - and in fact, if I partially emptied the rear tank (by disconnecting the solenoids on the sill tanks) then it would refill and I could watch the fuel gauge go up while I was driving There weren't any non-return valves as I didn't know, and the guy that sold me the kit and extra tanks didn't tell me - since I did my course I now now and fitted some check valves.
On my mates Range Rover installations, the two 40l tanks would always empty in a specific order - IIRC on one of them we had to move the sender to the other tank as it was on the 'wrong one' at first and the lights went off quickly rather than when the second tank was going down.
On my 110, the side tank always empties before the rear.
I'd speculate that it's a combination of :
a) How much heat from the engine bay reaches a particular tank - the sill tanks on the Disco probably got very slightly warmer than the rear tank.
b) Difference in spring strength in the check valves. Everything else being equal, whichever valve open more easily will determine which tank empties first.

The aftermarket petrol tank you have is a common fitment. The original Land Rover pump and level arm assembly is re-used with these. But it's a tight squeeze, and sometimes the float arm drags against the inside of the tank. Probably just wants a little bending, but removal of the tank is not straightforward ... depending how it was mounted it may require removal of gas tanks first ...

The other thing is how the float arm got bent when re-shaping it to fit in the smaller tank. IIRC the 110 and Range Rover conversions I've done all needed the float arm shortening by bending a zig-zag in it - it would be easy to bend it down and have it always read high.

I'd definitely agree with the advice to "enjoy", a V8 makes a Disco a much nicer motor than one with a concrete mixer engine in it

[stbb]

I will have to look at what tank has the sender on it. What causes the car to switch back to petrol? Is it the gas pressure in line going to engine bay or does it come from redings in tank ot guage. I ran it down this week , ignoring the empty tank leval and got to 180 mile before i decided to refill. I still have about 10l of gas ( usally only get 62 into 2x40l tanks).It was still runing on gas ok.

[SimonHobson]

What causes the car to switch back to petrol? Is it the gas pressure in line going to engine bay or does it come from redings in tank ot guage.

Normally (on an injection system) it's done on gas pressure, but there are other triggers that can be used. Most likely, it's a "oops, can't keep the gas flowing properly, switch back to petrol" safety feature in the system that's doing it.