Fuel gauge readings

[Apiarist]

Having referred to the great deal of help given to others with fuel gauge issues I’ve carried out some of the suggested tests and got to the point where I think I’ve found the problem but should mention I’ve limited understanding of car electrics.

The car is a 1968 1098 Traveller with the black face fuel gauge. So far as I’m aware the fuel tank and sender unit are original.
The problem is that with a full tank the gauge barely leaves the empty mark.

What I’ve tried so far:

a) With ignition on and wiring disconnected from tank sender unit and ‘shorted’ to earth the fuel gauge moved fairly quickly to the full mark.

b) With ignition on, voltage at the disconnected wiring to the tank sender unit was measured at 9v but the needle (analogue meter) wavered slightly, back and forth, over the 9v reading.
A test lamp between the disconnected wire and earth glowed fairly brightly but ‘pulsed’ on and off while the fuel gauge slowly began to rise.

c) As in b) but now with wiring reconnected to the sender unit: voltage was measured at 6.5 – 7v, again not a steady reading.
The test lamp glowed less brightly but otherwise as in b).

d) Resistance of the sender unit with wiring disconnected measured at approx. 220 ohms which I think I recall seeing somewhere indicates a near empty tank, which it’s not.

I think these tests might point to a sender unit float stuck in a low position but want to avoid jumping to conclusions.
And so I’d be very grateful if anyone better qualified thinks I’m on the right track or thinks I should make other tests (I’ve not tested the fuel gauge itself).

Many thanks

[firedrake1942]

It sounds very like it with those readings.

Years ago I had a similar problem and went straight for the sender unit as a starting point. Once taken out the float arm showed some resistance but freed quite quickly and moving it up and down out of the tank induced the petrol gauge needle to move as it should.

My next problem was the gasket as in 1980 these were an absolute sod to find and I ended up fabricating my own out of gasket paper- its still there !

[Apiarist]

Many thanks for prompt response firedrake
I'll probably get a new sender, don't think they're too pricey, as I can only work on the car every other week and it might avoid prolonging things if the old unit isn't fixable. I'll also feel happier the least time I spend over an open fuel tank, even if taking the obvious precautions!
Thanks again.

[firedrake1942]

Make sure you get the right one, I believe they change when the speedo colour / tank sizes / engine size changed about 1963.

[ManyMinors]

There is no choice of sender units available new is there? If the car is 1968 it will be fine as it is only the later units (to suit the black gauges) which are made now I believe.
The tank size remained unchanged in 1963 when the 1098cc engine was introduced.

[firedrake1942]

You are right the tank size changed from 5 1/2 to 61/2 gallons in 1957.

[Apiarist]

Thanks for all input.
ESM supply two versions, one pre Oct '64 and the other from then.
My Traveller (wife's really) is '68 and I'm fairly sure has original tank so hopefully I'll be ok with later version. Big difference in price between the two!
Thanks again for all response, it's really appreciated.

[ManyMinors]

Every day is a learning day The early unit didn't used to be available new and must be a fairly recent addition. The early one has a screw-on terminal and the later one is a push-on "Lucar" terminal. The tanks themselves are not different, just the unit. Your 1968 car will be the later (and thankfully, cheaper) type.

[Apiarist]

Well, I've ordered the sender plus gasket from ESM so should have it by Monday (might even be tomorrow if Royal Mail is feeling efficient - not holding breath though!).
As the car is not at home I won't be able to change the unit until Monday week (19th) at the earliest but I'll report back on whether it fixes the problem.

Cheers

[firedrake1942]

Before you fit the new one, see if you can free up the old. It may not be necessary to swap it out. Mine is still going after 30 odd years.

[Apiarist]

Yes, I think I'll do that. If it does work it should save having to mess around with adjusting the float level on the new sender.
Apparently it's possible the float arm would need bending a little so that the sender causes an accurate reading at the gauge.
Makes sense, I think!

Perhaps another spare part for the 'maybe it'll come in handy later' box?

Best wishes

[Apiarist]

Well, I’m glad to say that the problem has been found and was due to a faulty sender unit. The float on the old unit was well and truly stuck in a low position, falsely causing an empty reading on the gauge.
As suggested, I freed the float arm on the old unit but this did not alter the resistance in the circuit and the gauge remained on empty.
In replacing the unit, the following events might be of interest (sorry if they’re not):

- Since the unit sits in a depression in the top of the tank I was aware that the fuel level might be higher
than the mounting point, with obvious results to be avoided! With no siphon kit (and not wanting a
mouthful) I reduced the fuel level via the tank drain plug. By chance this left the fuel exactly level with the
unit mounting point.
- The first attempt at fitting found that the float arm would need adjusting to give a more accurate reading
and so the unit was removed.
- The second fitting (you’ve guessed it) found that I’d over adjusted the arm.
- When attempting the third fitting, I found that the cork gasket had got so wet with fuel that it no longer
fitted and had to be dried before it could be used again. In the meantime I lowered the fuel level some
more to avoid a repetition.
- At the third attempt the gauge gave a reasonably accurate reading but (what now!) there was a leak
around the unit seating when the fuel level was moved around to test the seal.
- Perhaps I’d not tightened the six bolts sufficiently (or evenly) but I decided I needed a sealant for a better
chance of preventing a leak, but what to use. After some research, and speaking to a techie help desk, I
decided on Loctite 5922 flange sealant, applied to all four surfaces.
- Wanting to give this time to set (it provides a breakable seal) I won’t test it until next with the car in
about two weeks.

By the way, the new unit came with a strangely shaped rubber ring around the float. ESM confirmed that all their units had these but couldn’t tell me what they’re for. My best guess was that it was meant to stop the float from hitting the top of the tank but since the old unit did not have one I left it off.

Best wishes to all.