Fuel Gauge Issues

Hello. Been a while. About 3 months ago my 30 year old fuel age got a mind of its own and started doing all sorts of weird things. I over filled the tank in the 100 degree GA heat in the Summer. The gauge went past the full mark. After about 150 miles later it came back down to 3/4 of a tank and worked fine. I don't drive her very much so it was about 2 months later I needed gas. I only pumped about 15 gallons in effort to avoid the same hang up issue. I got gas again last week and I only pumped 10 gallons in the tank from about 1/4 a tank. Now the gauge has went up passed full again. Any ideas what is causing this. I've heard sending unit, too much pressure in the tank at fill up, a sticking float or bad gauge. Thank you.

See if the oil ressure ansd temp gauges also rise when the fuel gauge seems higher than it should be. If they up and down together, then the issue is the IVR (instrument voltage regulator) and not the fuel gauge system.See http://turbotbird.com/techinfo/gauge_flux.htm. If it is just gauge misbehaving then see this post: http://natomessageboard.com/ubbthreads.p...Post253076

Thank you. Yes it is just the fuel gauge.

Thanks Pete D. Yep, I'm guessing it is the IVR. Yesterday I noticed the temp and op gauge were nearly at HOT. I always keep an eye on these during normal city driving. When I would come to stop they would fall back to normal-gradually at idle for 5 or so minutes. Still having fuel gauge issues too. Do these IVR's go out a once or is it a gradual thing. I've been having these issues since August. Yesterday was the 1st time for the temp and op gauge. Thank you.

Those mechanical IVRs are a legacy from the 1960s or even earlier. They are a primitive mechanical version of PWM control where a bimetallic strip that conducts the current that go to the gauges opens and closes a circuit once every second or so to regulate the average voltage applied to the gauges to 5 Volts. The bimetallic strips contacts stick shut, causing the gauges to receive more voltage making them go up. Eventually the contacts unstick on their own, and sometimes a good swat to the dash can unstick the contacts.

New mechanical IVRs arent cheap and will fail again due to their ancient design. I built myself solid state versions years go for my older Fords that last forever. I think you can find solid state IVRs online (Ebay, etc) for Fords for 1/3 the price of the POS mechanical ones and they will last the life of the car.