Anyone have this fuel gauge problem?

[OneHalfMex]

I've had my truck ('69) for a few years now and up until yesterday I thought it had a 12 gallon tank (behind the seat tank) in it... I would drive the truck until the gauge read empty and then when I went to fill it up the pump would shut off after ~11 gallons. Then when I cranked up the truck the fuel gauge would be on full, so I just assumed the trucks tank was ~12 gallons.

Yesterday I found a pin size leak in the tank. When I went to order a new Spectra Premium tank I realized that my old one was 20 gallons. Any ideas why the gauge would have been acting this way?

Thanks,
Jonas

[red71cheyenne]

Sounds like your sending unit is off or the guage is off or both. The sending unit is 90 ohms and if you get a new one you can hook it up prior to install and test the guage out to see if it tracks. If it doesn't, you may need to check the resistor on the back of the guage or just replace the guage with a used one that tests good.

[OneHalfMex]

Is the resistor on the gauge supposed to be 90 ohms as well?

Also, if I haven't really had any problems besides the gauge reading incorrectly, is it good to replace the sending unit while I'm replacing the tank? Or is it more of a if it isn't broke, don't fix it?

Thanks!

[red71cheyenne]

Not sure on the resistance on the resistor, I was thinking it was 150 Ohms. You should check the sender to verify its not the problem when you replace your tank. Also a good time to replace the sock and check the float to make sure its not leaking. This way you know that all is good when you put it back in and can further isolate why your guage is reading wrong.

[Lee H]

Mine truck literally runs out of gas at the 1/4 mark. I always filler it up at the 1/2 mark or before. Been tha way for many years. No big deal, not worth worrying about, to me anyway.

[VetteVet]

You should test your fuel gauge and the sender for the proper resistance and operation.
Find the fuel gauge wire on the fuse panel and unplug it. It will be on the end by the flasher.It's a tan or light brown wire.



Turn on the key and the fuel gauge should go to the right past full to the 3:00 position.
Jump a wire from the fuel gauge terminal to a good ground and the gauge should go to empty. Key still on.
If it does these two things then the gauge is good. the resistor resistor readings should be between 35 and 40 ohms.


The fuel tank sender should read 0 to 90 ohms when the float arm is cycled through it's travel. I suspect that the arm may be bent down and is going to empty sooner than it should. Most gas gauges will read full or a little past full when the tank is filled because the sender arm reaches full travel before the tank is full.

[OneHalfMex]

Thanks VetteVet! The pics and description are very helpful to someone like me. This board is amazing!!!!