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Gas gauge problem

Started by june2021, June 22, 2021, 09:51:21 PM

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I have a 1975 MGB Roadster. When my gas tank if full the gas gauge registers 1/2 full. I have replaced the sending unit as well as the gauge itself and have the same result. I have also jumped the wiring (ground wire etc.) also with the same result. Could there be an obstruction in the tank preventing the float from full movement? Any advice would be appreciated. Don Pohlmann


Hi Don,

With all you've done up to now, I'd start by again checking the wiring over its entire length from the tank to the instrument panel.  Make sure the gage and sender are properly grounded.

Damaged insulation or a pinched wire could cause a ground which might throw-off the signal and reading.  Your car is over 45 years old and these things do happen.

If you have the OEM gas tank still installed, it would have baffles internally. Maybe one is loose in then tank that is restricting the float's movement.  Problem is that the only way to check that is to drain the fuel, remove the sender and then fish around the inside of the tank to see if anything is in the way.  Almost as much work as replacing it.

I also see there are several sending units listed for later cars, so make sure you have the right one.  The (3) tanks listed as the same for 65-up, just different suppliers and the OEM style is baffled, so I doubt the fit with any is an issue, but see my comment earlier on the baffles. 

Hope that helps you.  Let us know what you find.

Safety Fast!


Art Isaacs
AMGBA Tech Staff


Thanks very much for your suggestions. I think I will wait till the driving season is over this fall to tackle this problem. Too much fun driving now. I have an endoscopic camera for checking inside walls. I think I will pull the sending unit and see what I can find.

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