The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge-Not Quite Full

1951 3600 12 volt system, with a runtz on the original gas gauge. The gauge will not read full under normal conditions.

The replacement sender checks 1.4 to 30.4 ohms. The Gauge will only go to full with the sender wire disconnected. Ground the wire and the gauge goes to empty.

With the sender out of the tank and the wires connected the gauge will read from empty to not quite 3/4. Disconnect the sender wire and reattach quickly and the gauge will read full and hold until the switch is turned off.

All of the above has been done with the truck wiring harness and with a seperate jumper to eleminate a wiring problem.

Any advice will be appreciated.


Jim

Try checking the gauge using a variable resistor (pot.) of around 0-100 ohms. Put it in place of the sender since that's what the sender really is. Might be a sticking gauge or the voltage you are sending to the gauge is not quite correct. Good luck

I'll be following this one closely as my 51 does something similar. I still have the old harness and sending unit, to be replaced one day.... Let us know if you get it resolved, ill probably need to troubleshoot mine when I get to it.

Thanks!

Today I used a jumper wire to the 12 volt side of the runtz to make sure it was getting full voltage. No change in function.

Beltfed, what exactly is a variable resistor and most importantly would I find one?

Thanks,
Jim

As the name implies, a potentiometer aka variable resistor is an electrical device which allows one to change the resistance in a circuit with a mechanical movement. Changing the volume on your radio or the fan speed on you truck heater, you do with your hand turning a variable resistor. Inside your gas tank, the sender changes its resistance using the float. The electrical current flowing through the gas gauge and sender varies according to the resistance of the sender. There are more types of pots (short for potentiometer) than "Carters got liver pills". In this case, you need one that covers the resistance of your sender. So 0-50 ohms or 0-100 ohms, 1/2 to 1 watt will handle it. It will cost a couple of bucks at "Radio Rhack" or a local electrical/electronic store. If you have a buddy who works on electrical stuff, he most likely has box of old ones sitting around and will give you one.

Thanks, I'll find one today.

sounds all to familiar my 66 fuel gage reads 1/2 full when the tank is in fact full of fuel.I've replace the sending unit twice w/ the same results. I've learned to live w/ it but would love to solve this problem.

Dave66, you could try the same thing as suggested to Farmer51. Other than a voltage source, wires and their connections, the only things left are the gauge and sender. As the old wise general said, "Divide and conquer". You will also need a VOM to measure the variable resistance (out of circuit) when the gauge reads what you want. Remember also, some gauge read full when there is zero resistance in the circuit, others read empty (ex. 0-90 ohms & 90-0 ohms).

It sounds to me like you won't get a full proper reading with the gauge that you have. That would be my guess.

The needle could be slightly bent. I tweaked mine upon disassembly and havent bothered to fix it yet. It still goes past full when testing, but it only goes up to about 2/3 - 3/4 when the tank is filled to the brim.

Jeff