Fuel gauge accuracy

I filled my 58 up with gas I had for the hurricane season here in Florida. I got a little to generous and the tank overflowed. I siphoned out enough to keep it from coming out the filler cap. I then got in the car and turned it on to check the gauge. The gauge showed the tank to be about a 1/16 from being full. I drove around a bit and saw some fuel around the cap were it must has sloshed out during my ride. I thought maybe I had an air pocket in the tank from my filling with the gas cans. However. the gauge still showed the tank to be below empty. Any way to check the gauge or the sending unit to see what is going on?

Thanks Wah2oo

Interesting. I have a 59 that when I fill it it goes slightly above the full mark. Thinking that if above the full mark when full must translate to empty before actually reaching the empty mark. My guess is that the arm on the sending unit needs to be bent down a little. In your case, it likely needs to be bent up a little. I don't think these gauges were ever meant be be all that accurate and likely each have somewhat of a personality but, I think by bending the arm up or down will probably improve the reading. I am sure that someone on this site is much more knowledgeable then me so, I am interested in hearing what others have to say as well.

Thanks,
Todd

Take out the sender unit from the tank, ground the unit, and move the arm up and down. Move it all the way up, have something or someone hold it, and check where the gauge is. If all the way up, shows FULL all the way, then bend the arm down a little.
If it won't go any higher, there is an issue with the gauge or sender unit.
I have heard of some people purposely bending them so that empty is actually not empty. But that will only be for a person who forgets to fill gas all the time and needs a reminder before it happens.

If it doesn't bug you, then there is no reason to change it.

I took the unit out with the tank full. It was still at 7/8 before I removed the unit. With the unit out and held fully up the gauge read 7/8 full. When I put it all the way down the gauge was exactly on empty. Is there a way to find out whether the gauge or the unit is the problem? I have an extra gauge which is in excellent shape but I am not sure how it works. Can I rig my extra gauge up to the unit in the trunk somehow to test it. I hate to buy a new unit if I do not have to or crawl around under the dash to get the gauge out then not be able to test it anyway.

Wah2oo

If you momentarily ground the yellow wire at the sending unit your fuel gauge on the dash should read full, if it doesn't the gauge is the problem.

Do what ford only said. Fully ground the wire to the body and see if the gauge works.

Check the other gauge you have with the wiring to your current gauge. Disconnect the wires from the guage in the car and use alligator clips with wires to connect to the other gauge. Just be sure to connect it the same as it was in the car.

Thanks, Is there a problem if you hold the ground too long? I noted Ford Only said momentarily. I will give it a try.

The gauge showed full when I grounded the yellow wire. Must be the sending unit. I removed it's cover but I see no way to fix anything in it. Any suggests whether to get a new one or find a good original used one?

Got a new sending unit with no improvement in gauge function. It still read full with the yellow wire grounded. I checked my extra gauge I had and it didn't seem to work at all. After a sleep and being out bid for a new gauge I checked my extra one again and found I had disconnected one of the wires from the regulator when working behind the dash. When I hooked the regulator up the extra gauge worked perfectly with my original and new sending unit. Now have an extra sending unit I guess the original gauge needed no resistance to show full, something the sending units didn't do . Anyone else have a gauge that malfunctioned like mine?

Wah2oo