Impossible to fill! (Suspect fuel gauge)

[TomLS]

Hi all,

No matter how much petrol I try and squeeze into Madge, the gauge won't go about 3/4 of a tank.
Not a particular problem, just a bit confusing / annoying.
If anyone can shed some light, it would be much appreciated

Tom.

[Alec]

Hello Tom,

the simple test is to disconnect the fuel sender cable at the tank end and touch it to a good clean earth with the ignition on, and if the voltage regulator and instrument is good, then the gauge will read full. (I don't know what year your car is but I think the very early ones work vice versa, i.e reads empty.) If that is the case then it is a problem sender or the tank is not properly earthed?
Try it and let us know the result?

Alec

[TomLS]

Cheers Alec.

Might have been helpful to know she's a 1970 Traveller. I will try that, but not now - it's raining elephants out there
The voltage regulator is believed to be ok, but I've just received a 10V fixed voltage regulator to replace it when I fit my 2 new gauges.
When I get a dry minute, I'll let you know!

[MarkyB]

It's all part of the character of the car, more interesting is how many miles can you do after the gauge reads empty.

[mike.perry]

If you are putting £43 worth of petrol in then you are filling the tank! (£45 by the end of the week). I could fill the tank on my Series MM for £3.56 when I bought it.

[bmcecosse]

Does the needle stick at 3/4 for ages, before eventually dropping as the fuel is used ? I suspect the float is sticking against the wall of the tank - possibly not fitted correctly in the top of the tank.....

[DAVIDMCCULLOUGH]

Or the float may have 'sunk' slightly. I had a late one which has the plastic type float that had a wee hole in it that let the petrol in and kept the float weighted down and not reading full!

[TomLS]

If you are putting £43 worth of petrol in then you are filling the tank! (£45 by the end of the week). I could fill the tank on my Series MM for £3.56 when I bought it.

A 'fill' for me has only been about £25 so far, obviously got a lot spare when the gauge reads empty!

Got some mucking around done today due to lovely weather, here's what I discovered:
-Running a lead from the -ve side of the battery to the feed from the float saw the gauge rocket to the 'F' position.
-The last numpty to remove the tank didn't replace a SINGLE screw, meaning it was bouncing around in the hole, and giving an unreliable earth. (Now replaced them all with 5mm self-tappers, should give plenty of earthing)
-The float had a tiny bit of fuel in it, so I found the pinhole, drilled it out, drilled another, blew the fuel out, then re-sealed the holes with a blow-torch (obviously well away from the tank )
-The sender arm moved freely and pointed from front to back (so not fouling on the tank wall).
-Cleaned the terminal and the spade connector.

The gauge still only reads 1/2 full, and the fuel level was only 2-3mm lower than the sender gasket (which I didn't think of before I unscrewed it!), but to my estimation that's still over 3/4 of its capacity.

So it seems the problem remains - any other clues? Or is a new sender the only remaining possibility?

Thanks for all the suggestions so far

[DaisyMayFozz]

[quote]A 'fill' for me has only been about £25 so far[quote]

same here

[MarkyB]

got a lot spare when the gauge reads empty

This is the interesting figure, you know when it's full, you just filled it!
When you about to run out, now that gets really interesting

[TomLS]

Well I haven't had the nerve to push my luck so far... The tanks are 6.5Gal right? (do Travellers and saloons have the same tank?)
So thats 29.5l.
At £1.35 per litre (grr ) that's £39.28 for a complete fill.

So I've been leaving £15 in the tank, believing it to be empty, so that's 11 litres which is about 85 miles!

Next time I'll not be so worried when the needle hits 'E'.

But mind you, I keep a 5l petrol can in the boot... just in case

[MarkyB]

Go for it!
Just avoid the Blackwall tunnel when you are testing the limits!

[Alec]

Hello Tom,

the other remaining thing is the integrity of the tank to body earth, if that is sound the all that's left is the sender unit.
I think the original screws are 2 BA, not self tappers?

Alec

[TomLS]

Hello Tom,

the other remaining thing is the integrity of the tank to body earth, if that is sound the all that's left is the sender unit.
I think the original screws are 2 BA, not self tappers?

Alec

I was assuming that the tank to body earth, created by the cutting of threads into the steel by the self tappers, would be more than sufficient - especially given that there are about 12-16 of them.

I had no way of checking the original fittment as there were no screws remaining to copy, so I decided self-tappers would be the easiest (and I had a plentiful supply to hand). They've done the trick, and are certainly better than no screws at all. Unless there's a particular reason to use the originals I'll be leaving the tappers.

Cheers,
Tom.

[TomLS]

P.S I tested the resistance of the earth from the bolts securing the sender to the -ve battery terminal using the same length of wire I used to check the gauge - and it was under 2 ohms. The multimeter has a probe-to-probe resistance of 0.6 ohms, so given the length of cable used, I don't think I have anything to worry about with the earth as it stands.

I guess the only thing to do now is to brim the tank one more time and see what the gauge does. If its no better then a new sender it is.

I can see from the pictures on ESM that the sender recommended for my 1970 (FUL102) doesn't look like the one I removed today. Does that mean the one in my tank is the original (and therefore 41 year old) sender, and that they "don't make 'em like they used to?" (It doesn't look like the early model one listed either).

Tom.

[Alec]

Hello Tom,
my mistake I misread your post, yes that would give a good earth connection I would think. If your sender doesn't look like the one on the ESM website, could that be the problem? It may be functioning but if the angle of the arm is such that it reaches the tank roof before the slider reaches the end of the resistance wire, i.e it is not intended for that tank?

Alec

[TomLS]

Hmm, don't know. I've looked on as many minor spares sites as I know (about 4) and none of them list a sender which looks like mine for either the saloon, traveller, van or pickup type tanks, but the float does look identical.
Rather than buy a new one I might just take it out and bend the wire a bit, then refill the tank. Might take a few attempts to get it right but it's a daily driver so I get through fuel quickly enough.

Failing that I'll have to shell out £20

[Alec]

Hello Tom,

well worth trying, although it may give an error at the low end if the arm is re bent?

Alec

[bmcecosse]

The 'low end' is where it matters! Who cares at the high end!

[MarkyB]

My point exactly!

It isn't impossible to fill at all, just impossible to get reading full on the fuel gauge, which isn't a big deal.