The fuel level reading involves two instruments, the dash gage and the tank sending unit. 12 VDC is applied to the gage which regulates it to a very small current (that is so the gas tank will not explode with a high current electrical discharge. Good idea huh?) The sending unit varies in resistance which increases the current for a full tank reading and decreases the current for an empty tank reading.
I investigated my 56 Dodge Custom Royal fuel level gage and found the following:
1. The sending unit was "plated" with a heavy layer of varnish. This is an insulator and blocks the low level current through the sending unit. This appears to the dash gage as an empty tank.
2. I carefully removed the cover around the potentiometer portion of the sending unit. I found inside a ceramic cone with high resistance nickel/chromium wire wound around it. The varnish was thick. The float arm was connected to a press formed metal wiper. This wiper moves up and down the resistor coil of wire changing the current seen by the dash gage. The resistance of the gage is about 100 Ohms. With the varnish, the resistance jumps to infinite in places.
3. Inspect the wire windings for wear where the wiper rubs, assuming the wiper arm is not worn through and the wire is OK, clean the assembly with carb cleaner or caustic soda dip cleaner and brush with soft brush until all varnish is gone. Be very careful to NOT break the wire or the unit is useless.
4. The dash gage is an intrinsically safe torque motor, basically. There is a transformer like winding which, when a current is passed through it from the sending unit, applies a torque to the needle of the gage indicating the fuel level. If the gage is the source of your problem, it is probably mechanical in nature. If it was electrical, the gage would not operate at all. Clean and sparingly lube the pivot point of the gage with a non gumming light oil. Gun oil mixed with alcohol works well. Less oil is better than more oil. ***CAUTION***WARNING***OTHER ATTENTION GETTING WORDS*** The wires on the gage are about the size of a human hair and are very fragile. Do not break the wires or the gage is lost. There are four wires that are difficult to see because they are so fine.
Based on your description, I would clean the sending unit and then check to see if the problem is fixed.
-----Original Message-----
From: Forward Look Mopar Discussion List [mailto:L-FORWARDLOOK@xxxxxxxxxxxxx] On Behalf Of eddee@xxxxxxxxxxxxx
Sent: Monday, June 18, 2012 7:34 AM
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Subject: [FWDLK] FUEL GAGE DIAGNOSIS
Hello Members
Concerning the 57/58 PLYMOUTH fuel level gage...................
I am wondering if the problem with it 'sticking' to an empty reading
after initial start up,,and always reading 'low' by about 1/2 a tank is
a gage issue as opposed to a tank level sensor issue??????????
Thanks for response
ED ECKERSON
PS--Anyone have experience with a gage rebuilder???
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