Replacement fuel gauges - different case spec?

[rswaffie]

Hello,
The fuel gauge in my 3.8 is not particularly accurate and erratic in behaviour (I’ve tried swapping the regulator for a solid state one and the sender was a new item). Looking at the offerings at SNG and Martin Robey, they come with separate plastic bulb holder and wiring. When I queried this with MR, they stated that the bulb holder is required because the gauge case is plastic and the original bulb holder won’t fit! Didn’t the original gauge Earth via the metal case? Does anyone know a supplier who supplies an original spec replacement? If not, I guess I’ll have to buy one of these to replace mine (minus bulb) whilst I take a chance and get mine refurbed?

[Gfhug]

Richard, could you not find a Smith’s fuel gauge on fleabay that would do service whilst you get yours overhauled? May not look exact but will do the job pro-tem.

Geoff

[rswaffie]

I did contemplate that, but I want a (in theory) known good one to confirm if it is actually the gauge, or if the new sender may be faulty.

[mgcjag]

How about a guage wizard.....fits between sender and guage to calibrate....Steve https://spiyda.com/fuel-gauge-wizard-mk3.html

[rswaffie]

Hmmm, that looks interesting. If they did a positive earth version it might be worth a try.
My gauge does the following:
I fill up at petrol station. Gauge reads full.
Sometimes, After about 10 miles it falls to 3/4 or 1/2.
Other times, it stays on full for at least 30 miles, then drops to 1/2 or 1/4.
If I then fill up again, it will take anything between £10 or £35 to reach full. So it seems to be under reading, but by varying degrees.

[44DHR]

Richard,
Is it definitely a fuel gauge fault ?
Are you sure that the fuel sender float in the fuel tank is correctly operating ?
I have just read that you have fitted a new sender, but can you check that it is not defective or taken in fuel. In other cases of failure, it is not unknown for these to be replaced with various designs of wine corks !
It’s easy to access and check the state of it.
Regards,
Dave

[Series1 Stu]

Hi Richard

My money would be on the sender, especially if you have a reliable voltage regulator. My aftermarket sender is one of the (even) more disappointing purchases. Its just some generic POS sent out as a DIY kit which probably took longer to set up than it would have taken to fix the original. I have only added fuel to the tank and run the engine for a short while and the gauge seemed to drop quickly but I haven't explored further.

It would be nice to be able to compare a known good original against an aftermarket one to check the sender outputs for various fuel levels.

I wonder if you and I have our float arms at the same length? I can't remember how I judged the length.

Regards

[rswaffie]

I bought the sender at the same time as the new fuel tank, from sng. It is this one:



As the gauge is the only ‘old’ item in the chain I thought I’d test it first. With the temp gauge you can put a specific voltage through it and see if the 3 test dot marks are in line with the needle. It may be the same for the fuel as I think it’s the same unit, with different face. I might try this if I can find the test voltages info.

[neal herridge]

Richard.
Caerbont Automtive Instruments is the firm you need to contact if you need new gauges.
They have all the original Smiths tooling & all the cases are steel as in the past.
The part number for the fuel gauge is BF2200-12 ,I have mixed their gauges with original ones & you can't tell.
Hope this helps Neal.

[rswaffie]

Cheers Neal. I’ve used them in the past so I’ll drop them an email. I don’t think they sell via their website if I recall.

[ralphr1780]

Richard, why not grabbing a used original one? Post in the wanted section, for sure you will get response, hopefully from UK based fellows.

[tim wood]

I purchased an oil pressure gauge direct from Caerbont to the original spec 60 psi max reading in mechanical format.
Spoke to them on the phone and very helpful indeed

Tim

[rswaffie]

Thanks all, I’ve confirmed with caerbont that theirs will be the correct spec and can use my existing bulb holder/wiring. I’m going to do a couple of tests first, then if I still suspect it’s faulty, I’ll replace it.

[rswaffie]

I’ve done a bit more testing, based on the fact that after filling up, the gauge read full but after 30 miles it was on half full.

1. Swapped out solid state vr for original and added extra earth connection to it and gauge just in case. Still read half full.
2. Added extra earth to sender. Still read half full.
3. Swapped sender connection from fuel to temp gauge (new) and still read half full.

So, it seems like the new sender is at fault. I was wondering if I had orientated it incorrectly in the tank. I used the sng parts diagram which suggests the float/arm should be pointing towards the rear of the car. Correct?
I know you can’t see the float in the pic, but their diag had the red & white connections at 12’clock as you look from the back of the car.
I tested the low fuel warning (earthed the wire) and that works ok.
So I guess I’ll get another and test it outside the tank first to see what happens.

[rswaffie]

Update:
I got a new sender from Martin Robey to replace the SNG item. Also had the new smiths gauge on hand just in case.
Swapped out the sender (Robey version feels more robust than the SNG version). Before swapping out, I checked the gauge to see what it was registering - 1/4 full. I knew this was wrong. After swapping it out - just over 1/2 full. Went to petrol station and put in 25L and it registered just under full. Went for a longish run and the needle hardly moved, whereas before it would have dropped by 1/4. Will go for a much longer run to see how it goes.
New gauge up for sale as now not needed!

[Gerry]

Hi Richard, don't worry about the positive earth changed mine to negative 20yrs ago never looked back.

Regards Gerry 62 ots Ontario Canada.

[MarekH]

It was always going to be the sender, as the gauges are all quite similar bar the faceplate.

It sounds to me like the SNGB sender can be improved in two ways. Firstly, if the pivot of the sender float has less freeplay, then there is less scope for it to move in anything other than one plane (so the float can't easily move to an erroneous height as fuel level changes) and can be tightened to have its movement dampened - there is no need for it to move any faster than the bimetallic strip/needle in the gauge can move. Secondly, the arm of the sender needs to be reasonably rigid also, otherwise it'll wag the pivot loose.

If I were SNGB, I'd also check where it actually pivots to when in the tank and if that corresponds to 240-40 ohms (if that is the right spec) empty to full, since you've implied it had too high a resistance at half full. If it is the right electrical spec, then the default amount of bend in the float arm (versus the wiper) is set incorrectly

kind regards
Marek

[rswaffie]

Further update: I’ve now driven a further 200 miles and the gauge needle movement from full to flickering low fuel light is much more steady and consistent. I filled up with 45 litres which means roughly 18 litres were remaining as the low fuel started to flicker, assuming a 63 litre tank, although there may be a couple of litres of unusable capacity.