Fleetwood Meadow

Gas Gauge Only Moves to 1/2

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On my ‘52 Cadillac I replaced the gas tank and sending unit. I ran out of gas because the unit wasn’t grounded. I took it out and checked the resistance and it tested well. It is adjusted so that when it is about to run out of gas the needle is on E. I put it back in and grounded it and it started reading the gas level. So I filled it the tank and it only read to 1/2 full. I used that gas and filled it again and it still only got up to 1/2 full. Do gauges operate on 6 or 12 volts specifically? Meaning, could this gauge be out of a ‘53 Cadillac, since ‘53 started 12 volts for Cadillac, or does it not matter the voltage in the gauge? Since my car is 6 volts, is there a way to make this gauge show full when the tank is full instead of 1/2 full?

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Update: when I first turned the key to on the gauge went up above half. But then I started it and moved the car a little down the driveway and it went below half again and didn’t go back up. 

283BE406-D9BD-411A-B939-5E76A7B4BB48.jpeg

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Posted (edited)

A GM gauge of that period is 0-30 ohms. Next time you have the tank full, measure from the gas tank sending wire to ground. Measure just the sending unit, disconnect the gauge from it. It should measure about 30 ohms or maybe more. If it says 15 ohms or so, the problem is still in the tank. If 30 ohms or more, the trouble is with the gauge.

 

Make sure the gauge also has a good ground.

 

Sending units are electrically the same on 6v and 12v GM cars up until roughly 1965.

 

These are balanced coil gauges, and are fairly insensitive to voltage, but all the way from 12v to 6v could be an issue. Yes, a 12v gauge would be different than a 6 volt gauge. It probably matters but I have not tried it.

 

Going the other way, using a 6v gauge in a 12v car, the gauge would draw too much current and I would worry about it burning out. Some people have got away with it. I don't know for how long.

Edited by Bloo (see edit history)

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I've been through this three times on three different cars.

On two out of three of the new senders the floats developed leaks....... :angry:

One brass float and one plastic float.

I was real happy........NOT....... 🤬

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Posted (edited)

No. It probably isn't the full 6 volts.

 

Tank is full now? Disconnect the sending unit, and measure Ohms from the terminal on the sending unit to ground. If it is 30 ohms or more, the problem is not in the tank. If it is something less, like 15 Ohms or so, the trouble is still in the tank.

 

 

Edited by Bloo (see edit history)
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To check dash unit disconnect wire on sending unit and keep it away from ground,  key on engine off the gauge needle should go to one end of the scale either full or empty. Next with the key still on ground the wire that went to the sending unit, gauge needle should go to the the opposite end of the scale. if the gauge responds correctly the sending unit or tank ground is bad. If gauge does not respond correctly it is either a bad voltage supply, bad wiring or a bad gauge itself.

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I'm with Bloo. You have to see how many ohms resistance you are seeing with the tank full. If you are not within the gauge parameters you will not get an accurate reading. In your case only 1/2 full.  Senders and gauges not being ohm matched is the most common issue I see with gas gauges after a bad ground at the sender.

 

Jeff

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I did a reading after filling up the tank and the gauge read a little below 1/2. I took the lead wire off, the gauge when the key was turned on read full indicating the gauge is working, and the ohm meter read 22 ohms. I connected the lead wire again and the gauge went to between 1/2 and 3/4. I jiggled the wire and the gauge stayed there. I took it for a ride and the gauge stayed in that spot. It is actually in the same spot as the original posted picture. 

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Well... Looks like you are taking the sending unit out again... :(

 

It is either hitting the top, or the float is sunk, or the sending unit is just plain bad. 22 ohms should be something a bit above half, so apparently your dash gauge is doing what it should.

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