MGB: fuel gauge testing question

Is it possible to bench test a fuel gauge?

Reason I ask is that my 71 GT came with a barrel-o-parts (really, a barrel!) and there is a Smiths fuel gauge among the items. The gauge in the car kind of works, but when the tank is full, it only reads slightly above 1/2 full. I've been setting the trip odometer when I fill up and after 200 miles or so, fill up again. As the PO died a few years ago and the car sat a while, from the spares he had, there were quite a few new items that were never installed. The fuel gauge was obtained via ebay and looked like it was used but not beat. I'd like to test it and make sure that the ebay one isn't already in the car replacing an even dicier gauge. Hope that ramble made sense.

[quote=smirkinwill]
The gauge in the car kind of works, but when the tank is full, it only reads slightly above 1/2 full.[/quote]

Mine does the same thing. It seems to otherwise work perfectly. I was forced to change the fuel tank in my car shortly after purchasing it, so I honestly can't recall if the problem existed prior to that or not.

Mine did that, except it read a quarter when full. I replaced my gas tank and sending unit it now works fine. It's probably your sending unit.

I dont know electrics very well but I'm sure there's a way.
You would have to vary the input somehow (resistors maybe) like a rheostat.
I'm thinking it would be best to hook up a known good sender to it and run it through
the range of motion.
Do a quick search in the Library and also try Dave Dubois' site.
RS

The library has articles on testing and adjusting both the fuel sender and the guage.

Specifically, to test a fuel gauge you can apply 12 volts to it and see if it steadily and fairly rapidly goes from Empty to Full. Take the power off the gauge right after it gets to full - your test is done at that point.

As others have said, if your gauge isn't reading right, it is most likely the sender. It could even be as simple as your sender's float being "gaslogged" (waterlogged with gas). Testing the sender is reasonably straightforward, too. The instructions others have mentioned will step you through it. As with all electrical gremlins, if you step through a proper troubleshooting "flowchart" of sorts, you can virtually always track down the problem.

I wrote a very detailed article on how to calibrate fuel and sender. Both should be done together. Its in the library.