Fuel/Temp Gauge issues

Packfan

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Ok, I know this has been discussed at length on many forums/ pages there never seems to be responses by the OP's how they fixed the issue. Here is my situation:
1974 Satellite. Car had been sitting for 10 years. Started and ran good. Fuel gauge was buried below "E". Temp gauge would slighty move towards "C". Fuel tank had rust in it so I replaced that as well as the sending unit. Cleaned up the contact points on the grounding strap and reattached at the tank. Fuel gauge would not move. Did a test by grounding the sending unit plug and fuel gauge never even budged. Next, held my test light on the temp sensor on the intake. The light pulses which I assume means the voltage limiter is working? Voltage shows it jumping from 0 to 5.2ish volts when pulsing. Next day, get in the car and the damn temp gauge does not budge a bit! Changed out the temp sender and.....nothing. Get this, last night I go for a ride and the fuel gauge starts working! It is full but only reads a quarter tank. Still no temp gauge but there are voltage pulses at the sending unit. What the heck is going on here!?
 

Jeff Erwin

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Not sure if you ever solved this but I just went through the same thing. Steady pulse on the temp sender, ground it and the gauge moves as it should but when the engine is running it barely moves. Then I noticed that after I turned the engine off and waited a few then turned the ignition to run it moved to the middle of the gauge. Moved back to barely moved when I started the engine and let it idle.

I have a 185 thermostat so it's not like it's running cold. Engine runs great. Now I'm wondering if the temp sensor is flaky or if there are different sensors available.
 

Packfan

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Hi Jeff. Yes, I did resolve my issues with the gauges. The original temp sender was flakey when I bought the car. I had another temp sender on the shelf that looked identical to the original so I installed it. Problem was even though it looked the same, it was for a totally different temp reading and did not jive with my gauge. Went to Napa and purchased the correct one for my actual car/engine and it worked great after that. To make things worse, I was working on the fuel tank at the same time I was tracking down the temp issue. Turns out that the brand new fuel sending unit I bought from Rock Auto did not work! I cleaned up the contacts on the old sender and stole the sock and float off the new one and made it work again. I made an extension wire for the fuel sending unit and put the tank back together outside the car. On my Satellite I was able to reach through the filler neck opening and work the sending unit and lightly tweaking the float arm so the gauge read perfectly empty/full. In the meantime I also replaced the voltage limiter to the solid state version to rule that out.
Turned out to be totally different issues that I was combining as one.
 

Jeff Erwin

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I was wondering if there were different temp sensors, I suspect I may have the wrong one for my 440 Have to investigate.

Thanks.
 

Packfan

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Sometimes with these old cars we overthink things! I think the correct sender with have you back in the game. Keep us posted! -Eric
 

fine69

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I’m not trying to beat this topic to death but I too am having issues with the fuel and temp gauges. I haven’t read anything thus far that gives a reason why these two gauges have interconnected trouble. The oil pressure never did work that well but I have an aftermarket one under the dash. Anyway, the gauges still work slightly but not like they used to. The temp shows up to 140 degrees and I know my big block wouldn’t run at 140 in siberia in January. When I filled up the other, the gauge showed I had less than a half tank. The ammeter still goes apeshit as it always has.
Any thoughts, friends?

7D11470B-1685-4101-99D6-D86A07592F2A.jpeg
 

Jeff Erwin

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The temp and fuel gauges work on a 'relative to ground' theory. If you find the wire that connects to your temp gauge and ground it against the engine block, the temp gauge should rise to the top (right). The same with the wire connected to your fuel sender back at the tank. Remove it and ground it, the gas gauge should rise to the 'full' position. If they don't you either have a wiring issue (bad wires) or a gauge problem. If they do react to ground you probably have a sensor (either temp or fuel sender) issue. You might be able to isolate a bad wire issue by attaching a separate ground wire to the gauge behind the dash and grounding it. If it works where the first test didn't you probably have a bad wire. I would first suspect the sensors.

Your alternator gauge being wonky should be looked into, you may have a larger wiring issue somewhere.
 

fine69

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That’s an excellent explanation thanks! Now all I need is you to come fix it for me haha
 

Jeff Erwin

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I actually ended up rewiring the entire car bumper to bumper. I got tired of chasing bad wires and shorts, the entire harness and bulkhead plug were shot. Shit ton of work (about 100 hours) but well worth it to me, everything works perfect now. Hightly recommended if you have a spare winter and $860 for a new wiring harness.
 

fine69

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Someday it would be great to restore the entire car but I’ll have to tinker for the time being. And I just got back from a cruise with my wife and son and the gauges just started working again about mid cruise. I guess I’ll just keep an eye on it and when it happens again I’ll get into it.
 

Mackman

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I've had a couple "correct" replacement temp sensors that aren't correct and don't agree with each other.
 

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