Fuel tank guage

Post by **Doug G** » Mon Jan 15, 2007 16:22

I thought that it was getting great milage - just sipping the gasoline (petrol).

Well the guage works . . . in that when you turn on the ignation the guage needle slowly goes from E all the way over to F.

Unfortunately that does not accurately represent the actual amount of fuel. Not by a long shot.

I looked into the fuel tank. It has the big cover. There was about 2 inches of fuel in the bottom. Not a problem in regarding running out of fuel.

The float appears to be behind a protective(?) panel in the tank.

I wonder if the float (if it has one)for the guage is stuck at the top of the tank.

However does anyone know what I should be looking at (first) in regard to correcting the reading?

Tim · Post by **Tim** » Mon Jan 15, 2007 23:07

Doug, there's any number of things that can go wrong with the gauge, but its useful to have a bit of understanding of how it works. The fuel gauge is a "resistance instrument". Inside the tank the float unit is a potentiometer, as the float rises and falls the resistance changes. The gauge has a tiny little heating element and a bimetal strip, which bends as it heats up and pushes the needle toward full. As the fuel level falls, the resistance of the float unit increases, and the voltage getting to the gauge drops. The little heating element cools and the bimetal strip relaxes pulling the needle towards empty.

Also in the system is a voltage regulator, which is an important little part that trys to ensure that the instruments get 10v not the variable 11-14v that the cars wiring normally carries.

Basically the instrument is a voltmeter. So anything that varies the voltage to it will make it change. A dud float (that sinks, has a bent wire or has a problem with the potentiometer) dodgy wiring between the float and the instrument, a dud instrument or a dud voltage regulator can all effect it. Also its possible to fit the float into the tank slightly rotated, rather than straight up and down.

Add to that the fact that they weren't ever very well calibrated to begin with and you stop being surprised when they don't work.

The float sensor can be removed by dropping the tank out and undoing the bayonet fitting that locks it in, on the front end of the tank. You can then use a multimeter t check its resistance across the range. Unfortunately I don't know what its meant to be.

For many years now I have carried an additional 5L reserve of fuel in the side pannier. I've used it many times.

Tim

Post by **Doug G** » Wed Jan 17, 2007 4:35

Tim wrote:For many years now I have carried an additional 5L reserve of fuel in the side pannier. I've used it many times.

Tim

Good idea.

brokenmoke · Post by **brokenmoke** » Fri Jun 01, 2007 11:42

I hope this helps.

Wombat · Post by **Wombat** » Fri Aug 17, 2007 11:27

If you need a new 10volt regulator I make an electronic one that replaces the mechanical vibrating original that fatigues after 25 or so years. Very stable output.

Post by **Doug G** » Sun Mar 16, 2008 1:22

10 volt? Shouldn't that be 12 volt ?

Tim · Post by **Tim** » Sun Mar 16, 2008 10:25

Mokes only nominally run at 12V, in use its somewhere between 11-14.5V. Thats not much good for instruments that work off voltage so it has to be regulated. In the old days all they could do was regulate it downwards, the electronics weren't good enough to regulate voltage upwards. The old Smiths 10V regulators are very clever but pretty terrible at regulating, all they do is cut in and out, outputting either 0 or 12(ish) volts, but averaging out to 10V.
Wombat's modern electronic regulators do give a constant 10V output but, it doesn't really matter because the old bi-metal instruments are so slow to react that you can't really see the on/off effect.

Tim

Post by **Nigel(no top)Sykes** » Mon Mar 17, 2008 20:08

I can't see what your problem is Doug ! If the gauge doesn't work, like you say - just look in the filler cap. If you run out of fuel,A. just walk home - it's sunny, or B. retire to the beach bar and await rescue

Tim · Post by **Tim** » Mon Mar 17, 2008 23:04

I'm hopeless at running out of fuel, even with a mostly functional fuel gauge. I have a little rectangular 5L plastic fuel can that fits perfectly in the side pannier. It gets a fair bit of use, but then its cold here for most of the year and we don't have beach bars to shelter in.

Tim

Post by **Doug G** » Mon Mar 17, 2008 23:27

Nigel(no top)Sykes wrote:I can't see what your problem is Doug ! If the gauge doesn't work, like you say - just look in the filler cap. If you run out of fuel,A. just walk home - it's sunny, or B. retire to the beach bar and await rescue

Have not run out of fuel but have had the engine overheat and the clutch overheat/slip/fail so I did what you advised and retired to the beach bar to allow engine to cool and arrange a tow.
SWMBO refused to drive her car and tow the Moke. Had to get a friend to drive it.

Post by **Nigel(no top)Sykes** » Tue Mar 18, 2008 19:11

Drive what ? Her car ?

Post by **Doug G** » Wed Mar 19, 2008 0:06

Nigel(no top)Sykes wrote:Drive what ? Her car ?

Of course her car. Couldn't trust him to drive (steer) my moke, now could I?

Post by **Nigel(no top)Sykes** » Wed Mar 19, 2008 20:43

Post by **Doug G** » Thu Mar 20, 2008 23:28

Nigel(no top)Sykes wrote:True

Absolutely

Post by **Nigel(no top)Sykes** » Fri Mar 21, 2008 17:46

coincidentally, my fuel gauge will not go over 3/4 even with the tank full to the brim. Its probably had the speedo changed at least once and the gearbox three times. I just live with it

At least when the gauge says empty I know its time to start looking for a filling station