Sending Unit bad?

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straightlinespeed

straightlinespeed

Sometimes I pretend to be normal
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Im trying to figure out whats wrong with my gas gauge. When I fill up it only goes up to 3/4 tank. It will not climb any higher than that. I have a dent in the bottom of my gas tank. Its a larger dent probably 8" across and is about 1 inch above one of the gas tank straps. Would that affect the sending unit operating properly? Or????
 
Bend the float rod down. Youll see a full tank but may never see empty.....;-) I dont think a dent would affect the sender.
 
pishta said:
Bend the float rod down. Youll see a full tank but may never see empty.....;-) I dont think a dent would affect the sender.
Click to expand...

Sure it will, depending on the size. A dent in the bottom moves a certain volume of gas higher up compared to the swing of the float arm (in other words, the float is floating higher compared to the actual volume of liquid). But it should make the gauge read higher, not low -- the dent is taking up space that would otherwise be occupied by gas.

You might want to test it by running the tank completely empty, then seeing how much gas you can fit in before it kicks off, noting at what point the fuel gauge stops going up. I realize that's a hassle...

If you don't know where the dent came from, here's something to think about: I once had the fuel tank "implode" -- it basically sucked itself flat. The circumstances were: 1) the vent pipe was clogged (unbeknownst to me), 2) I ran the tank down below 1/4 on a very hot day, 3) I parked the car overnight at high altitude, and (4) the temp dropped into the 40s. All the vapor in the tank condensed into liquid, creating an instant vacuum. I was confused the next morning when the gauge read over 1/2, then when I stopped at the gas station, I could only put in 2 gallons. This made me look underneath. Oops.
 
Oh, it occurs to me that one reason for it reading low might be that the float is sinking -- it has developed a pinhole and is filling up with gas, floating lower than it should. It may have air trapped in the upper part, preventing it from sinking entirely.
 
Ok, I get the pin hole in the float. Right now that makes the most sense. I would like to get the dent out of the tank so of course Im going to have to drop the tank. Do you think I would be able to push the dent out with a pipe or something. Any other ideas? I thought about replacing the sending unit at that time. Although I suppose I could run the float up and down and watch my gauge to see if that changes.

I just wasnt sure if its possible for the actual gauge to fail
 
straightlinespeed said:
Im trying to figure out whats wrong with my gas gauge. When I fill up it only goes up to 3/4 tank. It will not climb any higher than that.
Click to expand...
i will trade you. mine reads 1/4 tank no matter how much gas is in it. ive done everything short of pulling the tank out. a giant PAIN lol
 
Just check the ohms +-7 open +-19 closed or the other way around. Either way your ohms should be between 7 and 19 if not its bad.
 
does your temperature gauge read correctly ?
If it is reading low also it could be your dash regulator
 
The ohms thing helps a lot! When I drop the tank I will check that out. As for my engine temp, yes that reads correctly.
 
To the hash marks on your stock gauge 10 ohms is full 73 ohms is empty.
Greater than 78 ohms = no needle movement from its home position.
Less than 9 ohms will overheat the gauge.

If a brass float has been bouncing against the bottom of a steel tank for a long period of time, of course it has a hole in it.
Dents in the tank can be corrected with air pressure and a rubber hammer. How much air pressure is a gamble. Enough p.s.i. to move the dent might sooner bust a seam.
Good luck with it.
 
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