Fuel gauge quit working after RTV went swimming

[Gary Fowler]

Earlier posted about how my RTV went for a swim in the pond and how I had to drain all the fluids.
Well the fuel gauge was the only thing that didn't work, so I purchased a new one and got it installed a couple days ago. The old one was stuck on full and now the new one goes to empty when the key is off but goes straight to full when the key is turned on. It has about 3/4 tank of fuel.
Question: Can someone explain what may have happened to make the fuel gauge stop working. No water got into the fuel, all the wires are still intact. It obviously is getting power.
I sure hope I dont have to replace the sending unit since it is quite tight to get to. Is there any way to test the sending unit to see if it is working properly. Likely have to remove it anyway since I topped off the tank after repairs while hoping that the float in the sending unit was maybe stuck.

 

[RNeumann]

I’d pull the new float out of the tank and hook it up where you can manually sweep it with the ignition on. It hopefully just needs some adjustment. But either way you will know if it’s the float. Typically sending units send varying amounts of resistance. So you can check the ohms up and down stream of the sending unit. I doubt you can find the specs so that info will only show if you are getting a smooth range or it’s jumping as the float position changes.

 

[PILOON]

Lots of those tank gauges are merely a wire wound resistor and the float moves a contact arm that sends the resistance value up to the gauge where it moves the needle based on the value.
Older senders merely used a cork float that could often absorb some water and result in false readings. Newer senders use plastics and are more stable.

You say 'after went swimming' so I'd suggest corrosion at grounding points and connectors should be the first places to suspect

 

[WranglerX]

Generally a gauge that goes to full no matter how much liquid in tank has open circuit between sender and gauge or bad sender...

Dale

 

[Gary Fowler]

Lots of those tank gauges are merely a wire wound resistor and the float moves a contact arm that sends the resistance value up to the gauge where it moves the needle based on the value.
Older senders merely used a cork float that could often absorb some water and result in false readings. Newer senders use plastics and are more stable.

You say 'after went swimming' so I'd suggest corrosion at grounding points and connectors should be the first places to suspect

I did check the connections, they aren't corroded nor loose. I was thinking that when the RTV took the nose dive off the pond bank that maybe the float was slammed into the top of the 3/4 full tank and jammed it. If it was plastic and broke, it surely would have sunk in the tank and showed empty rather than full. It was immersed in fresh rainwater so nothing should have corroded in the couple hours it was in the water and the fuel gauge didn't work when I got it out of the water, so not likely it corroded in that length of time. I suppose my next chore is to remove the sending unit. It is a bit cramped to work and barely reachable. I just have to price a new one and see what it costs. I cant see that any wiring would have been damaged but who knows.

 

[Gary Fowler]

After looking at some youtube on how to remove the sensor, I decided on the simply fix first. I simple got a long piece of wire, ran it into the tank fishing it along the top till I felt it touch the float, pressed down the float and the fuel gauge went to empty and back to full when I released it. It looks to be working but only time will tell if it is correctly registering. The tank is completely full now and it will take a month or so to empty it down since it doesn't get any long distance use this time of year and I am not inclined to siphon out the diesel to see where it shows empty. It previously showed E when it was very low or none (I ran it out to point of not running when on a slope ) so we shall see.
Dang, looks like I may have lucked out a bit. I am not sure now that the old gauge was not working right but it did have some condensation on the face so it likely wouldn't have worked for very long.