1950s '54 series 62 fuel gauge off by half a tank....

[Julien Abrahams]

The other day I wanted to go for a drive assuming that I still had half a tank of gasoline. However, I soon discovered that half a tank on the gauge means empty....
Here is what I have checked:
- Disconnected the wire from the sending unit. Gauge goes to beyend full.
- Run a wire to ground from the gauge (where normally the sending unit wire connects). Gauge goes to Empty.
- Removed the sending unit from the tank and measured its resistance. The resistance goes from 0 to 33 ohms, and does not jump around, which is right where it should be.
- Connected the sending unit to the gauge and grounded the body of the sending unit. Moving the sending unit by hand and watching the gauge. Gauge and position of the sending unit correspond (sending unit up, gauge reads full. Slowly lowering the float arm, gauge slowly goes to empty.
- Completely drained the fuel tank (by disconnecting the fuel line) and installed the sending unit. Installed an extra ground wire from the body of the sending unit to the frame. Ground is good (measured the resistance from the body of the sending unit directly to the negative battery terminal).

BUT: even when the fuel tank was completely empty, the gauge showed half a tank.

It appears that the gauge and the sending unit work fine when outside of the tank.
So, now my theory is that the fuel tank has been dented, right at the point where the sending unit is mounted.
Is that a valid theory?  The first picture is from the driver's side (where the sending unit is mounted.
I made made two pictures. Does they support my theory or is something else going on? Thoughts?
Thank you in advance.

[The Tassie Devil(le)]

Looks like that tank has had more hits than the Beatles.

Any deformation of the underside of the tank in that location will affect the pickup as well.

Bruce.

[Jeff Rosansky CLC #28373]

So when it appeared to be out of gas, did you drain it? I'm wondering how much was actually in there.
There is a pickup tube in the tank if I remember correctly. It probably has a hole in it.
Our 55 is that way. When it gets below about half, it starts starving for fuel. I think it's because the pickup tube has a hole in it.
I can still get an easy 100 miles or so out of it so I just usually keep it full.
Been that way for about 5 years now.