My fuel gauge fluctuates once it gets below approximately 3/8 full. It will climb to full and then fall to empty or anywhere in between in a matter of seconds. It seems to read properly when the fuel tank is above 1/2 full. Does anyone know what causes this and what I can do to correct it?

 

mine used to do the same. Your float in your tank. Thats what the problem is. i think could be something else but there are not baffles in these older trucks so the fuel just sloshes around like a thanksgiving macys day parade float does when the barely touches it. so my guess would be your float. i would say worry about your fuel when it gets around E and stays there! that would mean that you would need fuel. but like i said i could be wrong

 

Could be a dead spot on the tank float, also, play with the wires on top of the tank, if you can reach them, and have someone watch the gauge.

 

My gauges never work since new. 86 e350 van. Ford told me the sender was on the pump and it wasn't covered. They are full of s---. But I still have not fixed it. I word guess its all in the tank. One of these days. Only been 26 years. I am now repairing the old bird so I just mit drop the tanks.
Chet