Failed tank gauge?

[Clifford Pope]

The final red LED came on, so I refilled at the next gas station. It took the expected amount, but on restarting the red light stayed on, instead of displaying 4 green lights.

Checking under the cover on the tank shows that the gauge itself is reading Nil. That must be wrong - 30 litres of LPG obviously went somewhere, and the car is running perfectly and I can smell no leaks.

So does that mean the gauge has failed, or simply stuck? Is it likely that going over a bump might jolt it back into operation, or do I need a new gauge?
Presumably that means the tank has to be emptied and the flange or whatever unbolted so that the unit can be replaced?

[rossko]

So does that mean the gauge has failed, or simply stuck? Is it likely that going over a bump might jolt it back into operation, or do I need a new gauge?

Probably not ; probably ; yes ; probably not.
If the float arm has fallen off or something, its a new multivalve assembly required.

[Clifford Pope]

I can't picture in detail how this gauge works. presumably rather like one in a petrol tank, but how are the moving parts sealed?
Is the needle directly connected to the movement inside the tank, or is it a magnetic connection? Is it possible that the needle alone has stuck, and can this be accessed without depressurising, eg by just detaching the glass somehow?

[rossko]

Is the needle directly connected to the movement inside the tank, or is it a magnetic connection? Is it possible that the needle alone has stuck, and can this be accessed without depressurising, eg by just detaching the glass somehow?

No ; yes. Yes, yes - one or two small screws

[SAD199]

I filled at an unfamiliar station whilst on holiday and my red light stayed on for the entire week of the holiday. Came back home, filled at the usual place and all my green lights were back on. I wouldn't worry about it, try another station. I think it's something to do with the fill pressure forcing the level indicator down?

[Clifford Pope]

Thanks both, that's useful stuff to know.

In fact, later in the day, the problem suddenly cleared and 3 green lights came on, with a corresponding reading at the tank. It's been fine since.

The theory that it was something to do with the refilling makes sense - I had just filled up, although at my usual (only) garage.
At least I know it's not the worst, and nothing has dropped off inside, although it does presumably point to the internal bit sticking rather than merely the needle.

[dory]

The fuel level LED indicators above my petrol/LPG switch used to work fine, but now they always indicate empty (single red light). The gauge on the tank in the boot still works fine, so I’m not sure where the fault is.

There are red, blue and black wires coming out of the multivalve. The black goes to earth so I have been measuring the resistance across the red and blue. It’s always 0 ohms regardless of how much fuel is in the tank. I’m pretty sure it should read 0 ohms when full and a specific amount (e.g. 90 ohms) when empty.

Where might the fault be and how can I fix it?

The gauge has the following markings: REG SENS. GPL AM 3763 - 4183 - 130 - B2

[dory]

OK, I've taken off the sender unit on the tank gauge. It has a transmitter and four little receivers that look like black LEDs. As the tank fills up the magnet on the tank gauge needle gradually moves out of the way of the four receivers. I have measured a a 5 volt supply to this optical sender unit on the tank when the car is running on LPG, which I'm guessing is the right amount. Interrupting the line of sight between the transmitter and the four little sensors with my finger makes no difference to the red and green LEDs on the instrument panel. This leads me to suspect that this sender unit has died. Anybody know how to test one?

[SimonHobson]

I can't picture in detail how this gauge works. presumably rather like one in a petrol tank, but how are the moving parts sealed?

It's magnetic. I posted a pic of a disassembled Emer multivalve in this thread, and you can see the internal half as the black "L" shaped item half way down on the right hand side. The magnet in this unit is the silver bit in the upper left end of it, and the float arm rotates it by means of a slot in the sticky out bit at the bottom right end of it.

All the setups I've seen have had something vaguely similar - something to turn the movement of a float arm into rotation, and a magnet to couple that to an indicator or gauge sender on the outside.

[rossko]

OK, I've taken off the sender unit on the tank gauge. It has a transmitter and four little receivers that look like black LEDs. ...

Coo, haven't seen one of those OMVL optical senders for a long time. I think you have done the test, and its failed. Finding a replacement might be difficult though.

[dory]

Thanks rossko. I can't find a replacement part on the Internet and OMVL aren't answering my email requests. Does anybody know if it's possible to fit a different make and model of sender to my existing multivalve, or am I going to have to drain the tank and fit a completely new multivalve? If the latter, can anybody recommend a unit that will give me a proper analogue fuel level reading rather than just four LEDs?

[SimonHobson]

If the latter, can anybody recommend a unit that will give me a proper analogue fuel level reading rather than just four LEDs?

I've never heard of, or seen, one. On the other hand, a couple of times I've pulled a sender apart and changed the resistors so that it would drive the fuel gauge already in the dash - and used a two pole switch so it switches the gauge as well as the fuel (these were carb systems and I didn't use the standard switch).

Worked fairly well on my Disco which had 4 hole tanks and fairly large senders, but was a lot more fiddly on my mates Series III which had a multivalve and the smaller sender (darn fiddly those small surface mount resistors). The latter also had the annoying 'feature' of going from 1/4 to empty on one step - so it was impossible to get anything in between.
It also only works with one tank. For multiple tanks I've designed some electronics but not got round to building it yet