64C2Vette

Forgive me if this has already been asked. I searched around and kept getting results of questions about the accuracy of the temp gauge. Anyway, I got a 64 corvette from my dad last spring that had been sitting in a barn for about the past 40 years. I am down to the last bits until it is safe to actually drive so I'm getting pretty excited! Since I have been in possession of the car, the temp gauge has always been sitting at around 140. The old radiator was bad so I figured there want enough coolant in the motor for the sending unit to get a temp reading. I haven't done more than start it to move it in my garage. I just bought a new radiator with electric fan and decided to make sure my temp gauge is working now that I have coolant in my system. With the motor cool, if I turn the key on, the gauge will very slowly drop to about 120, and when I turn the key off, it will go back to the 140. If I disconnect the wire from the sending unit, I get the exact same reading. Touching the unhooked sending wire to the motor doesn't change anything. Now when I pulled the wire off, I noticed that the connector is very dirty and only hanging on by a few wires, but I thought if there was nothing hooked up to it, it would at least change the reading on the gauge. I'm going to work on it tonight to finish wiring the fan and want to take a look into why my gauge would be acting this way. As of now, my plan is to cut the connector off, try to gently un-crimp it so I can get the old wire out, clean it up, and re-crimp it to the wire. If that doesn't work, I do have an extra sending unit I can try. I haven't read the ohms from the sending unit yet but that is on my list to try.

Does anyone have any advice on what other steps I need to take to diagnose what exactly is wrong? Would a bad connection at the connector cause this behavior? Any help is greatly appreciated!

I also would like to say that I love all of you for the time you take to answer questions. I read the forum at least a few times a week but don't really feel like I have much to contribute at this time because I'm so new. However, when redoing all of the suspension, brakes, trailing arms, etc. I can't think of many times where a quick google to my problem, didn't lead me to a very detailed solution already posted on here. Amazing!

65 Pro Vette

Did you take the wire from the sending unit disconnect it turn the key on and ground it. That should send the gauge all the way up if it doesn't move you have a problem with the wire between the sender and the gauge or power to the gauge or just a bad gauge.

64C2Vette

I did a really quick trial of that last night but I'll have to try again tonight. I was actually laying in bed thinking about it and I wasn't going to be able to sleep until I tried that. I didn't have a helper so I just had to try and look while I held it against something grounded. I'll attempt it again tonight. I will also check power to the gauge tonight. I assumed there was power because it does move down about 20 degrees when I turn the key on.

0Willcox Corvette

If you remove the sender wire, with the key on the gauge should go to cool... Then ground it out and it should peg hot.

Clean the connector by all means and clean the terminal. Corrosion will add resistance to the circuit.

Did you replace the sending unit on the car or is it the original?

Here is all I have posted on my site about the temperature gauge for a 1964....

Here is our calibration chart for the 1963-1964 temperature gauge. So if you wanted to test your dash unit you could order online an adjustable potentiometer and use it for input to see if the dash unit is working. Or you could test it with by taking two flashers (they usually ohm out at about 50 ohms) in a series and that should put you at the second mark (or close).



-Willcox

64C2Vette

I haven't replaced anything yet. I bought one and planned on installing it, but then I read on here about all of the issues people were having with getting one that would be accurate so I thought I would test mine first. I will clean the connector off and try to get a good connection between the wire and connector first. I'm afraid it's going to break when trying to un-crimp it. If that doesn't help, I will hook it up to a pot and see if the gauge moves. Thank you for that chart! It looks like you sell that sending unit wire if I need it correct? I'm kind of new to corvettes so I wasn't familiar with your business but it looks like you are in Indiana. I'm a Hoosier as well!

TJefferson2020

I may have an original 64 temp gauge if you need one.

64C2Vette

Alright I will let you know if I get to that point. Hoping it's something else but will have to do some more diagnostics first.

0Willcox Corvette

If you break the terminal or wire don't worry about it.. Yes I do sell the wire but you don't need it if you break the harness at the connector. You can un-pin the terminal and just purchase the actual terminal and re-use the old connector.

Here is the terminal, and below that is how you un-pin it.
https://willcoxcorvette.com/corvette...imp-on-locking