1959 Cadillac Fuel Gauge Problem

[idaholc]

I recently purchased a barn fresh '59 series 62 coupe that had been sitting for 25 years.  I removed the gas tank and had it cleaned and lined.  I replaced the existing sending unit with new gasket and reinstalled the tank.  The fuel gauge needle now is pegged past full when ignition is on.   There is only a couple of gallons of gas in the unit.  Any tips on how to check gauge and sender?  I do not relish dropping that tank again and wrestling with the filler spout, straps, etc.  I guess replacing the gauge would be the easiest check, but I would hate to ruin another gauge if I shorted something out at the sender or something.

B. Goodnight

[jeremy9146]

Well Bill I'm afraid that there is a short in the wire coming from the sending unit and you'll probably have to drop the tank again.  If the gauge didn't peg before you removed the tank and replaced the sender chances are the gauge is ok.  Let us know what you find. 

Jeremy Weiss

[Dave Shepherd]

Actually a full tank reading usually indicates an open circuit. wire is disconnected or cut somwhere.

[Scot Minesinger]

Before dropping tank again (I Know what a pain, just did it on my Caddy) check ground.  Car electrical grounding is not always straightforward.  Is it possible the new gasket insulated the ground?  If there is anyway you can check the wire from gauge to sender is good that may prevent dropping the tank.

[bcroe]

Grounding is highly suspect.  Try grounding that wire fro the gauge to the tank.  If the gauge drops
to empty, the problem is an open circuit at the tank end.  Usually tank units have a ground wire so
as not to depend on random metal contact.  Try just grounding the tank before pulling it.  I once
drilled a little hole in a folded over tank corner, bolted on a ground wire, and used it that way for
the life of the car.  good luck, Bruce Roe

[idaholc]

The more I think about it, grounding could be the issue.  After I took the tank out and had it cleaned and lined I painted it with POR15 and used exhaust wrap to mechanically cushion the straps from the tank (1" rolled strips).  So there may not be a good ground.  I will ground it and see what happens to the gauge.  I will keep you all posted, hopefully to provide some satisfaction for correct advice.  I am currently out of town and won't be able to check till mid-week.

[Blade]

Bill,

This post might also be helpful for you, another owner had the same problem and wrote up a pretty nice guide on how to repair it:

http://forums.cadillaclasalleclub.org/index.php?topic=120183.0

Regards,
-Tibor