For (literally) decades I've been driving around with a non-functioning fuel gauge. In the early days it would show full for about 150 miles, then plunge to empty and stay there. Then it started showing about half full for half the time, these days the needle stays sullenly at the minimum position and never moves at all. It's never really bothered me as I go by range using the tripmeter, but I am going to be replacing my fuel line this winter with PTFE lined stuff and proper AN fittings so I thought I should fix the fuel gauge at the same time.

So the question is: What should the fuel gauge be showing when the sender is at the ends of its travel? I thought the European 'standard' was 10 Ohms Empty, 180 Ohms full, but the fuel senders from places like SVC show 20 / 200. To be frank, the traditional float on a bent bit of wire sender units look to be a bit crap really, whereas Car Builder Solutions have a much tricker looking stainless steel jobbie that is 0 / 180 that looks like it might be a better option altogether.

But of course first I have to measure what my current sender is actually doing, and if that's ok I need to figure out what my gauge is actually responding to (or not) to see if it's sender or gauge (or wiring betwixt the two) that is the problem.

So if someone knows what the Smiths gauges are calibrated to (or should be) it would help enormously.

TIA

My old type fuel sender unit in my mid 80`s +8 seems to work rather well and has done during my tenure as owner. I have run with it displaying very close to empty while touring in times past and when I fill it up it tops the scale all despite it`s ancient technology.. (-:

I have replaced some fuel related kit in recent years due to age and hardening, the most recent of which were the two tubes connecting the filler caps to the tank, replaced a couple of years ago or so, and as it is a habit of mine to fill to the brim when storing, I begin to wonder about the possible effects of the fuel on those hoses too..Hmm..? I tend to use BP ultimate which may be E5 or less, I think I read that different companies may have no bio content dependant on the region where the fuel is bought though the pumps will still be labelled as E5 ..?

Currently sitting about a gallon of full, that I pumped out for the lawnmower... The gauge is showing just off full, and happy to measure the resistance as is, if that might be thought to help..?

Thanks George. I have no problem measuring the actual resistance in my sender unit, I'm more concerned with knowing what resistance range the gauge is calibrated to expect.

I can measure my current fuel gauge by observing the needle deflection at a range of specific resistances, say every 20 Ohms or whatever, but that still wouldn't tell me what it _should_ be - hence the question.

Sorry, I thought a pic of the gauge read out ( whatever that might be) along with the resistance measured with that read out might have been of some use..

Tim I had a similar prob when showing full and did this to calibrate the gauge.

If it's the bi-metallic strip type instrument(s) which require a 10 volt instrument regulator, then resistance should be high at empty and low at full to exercise the strip with highest current/heat/deflection of needle. Unless you want super accuracy I wouldn't worry too much about the resistance range as long as it works as above.

FWIW the type above, introduced in the mid/late 60's were preceeded by the moving iron type which gave instant reading with no requirement for regulator, but bounced around a lot by the same token as fuel sloshed around in tank. These required a sender working in reverse with low resistance for empty. This allowed an easy check of gauge as disconnecting sender lead would have needle showing above full and touching lead to ground, below empty.

Richard, thanks for the much needed refresher on on test procedures for the bi-metallic strip type of gauge operation, and which which mine may be as I have the old style voltage regulator noted when I was messing around behind the dash some time back... I bought the last regulator in stock at the local auto electrics and general component supplier perhaps 15 or more years ago when buying up Lucas spares for my +8..

No worries about instrument regulators George, the OE electro-mechanical and superior solid state type are both available on eBay.

The test described was for earlier moving iron gauges BTW. Don't try it with bi-metallic type!

Tim, splice one of these in https://spiyda.com/fuel-gauge-wizard-mk3.html

The maker / designer, Chris, is based in the midlands and really helpful