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Erratic Fuel Gage?

Piper J3

Well Known Member
Last summer I recalibrated my D-180 fuel gage because readings no longer agreed with the Moeller fuel gage in the top of the tank. As levels in the tank approached ?-? the D-180 would show an addition 2-3 gallons. After recalibrating I thought things were going well until a week ago, when at the beginning of flight, the D-180 showed zero when there was 8 gallons in the tank. By chance, I reached behind the seat back to see if the electrical connection to the fuel sender was loose. The connector was tight but when I put pressure against it the D-180 fuel gage began reading upscale.

I checked the screw which holds the ring terminal to the fuel tank sender and it was tight. I removed the screw to examine the connection surfaces and they looked clean. I used electrical contact cleaner and lubricant on all the surfaces and reassembled. Works perfect now with total agreement with the mechanical Moeller gage.

So, what caused this problem? There are times in early spring when weather conditions allow moisture to condense on everything in the hanger. I have seen water dripping of the bottom of the wings and the hanger floor so slippery you?d think you were walking on ice. I suspect that moisture caused surface corrosion on the electrical contact surfaces.
 
The fuel sender should have a dedicated ground wire connected to an airframe ground and a fuel sender mounting plate screw with star washer. The intermittent problem that you experienced is likely due to a poor ground.
 
The fuel sender should have a dedicated ground wire connected to an airframe ground and a fuel sender mounting plate screw with star washer. The intermittent problem that you experienced is likely due to a poor ground.

Joe - that is what I originally thought. I added ground wires several months back and now the connection to the sender itself showed to be the root cause of my problem. Using aluminum airframe as common ground is problematic...
 
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