The temperature gauge in my 75 stays very low.  I had replaced the sending unit last year, but it seems there are a lot of ones to choose from -- not sure if the one I have is correct (I got it at a local parts house, so who knows. . .).   I have a second mechanical one under the hood which works correctly,  so I know the water does heat to 180 okay.

Some of the parts stores products are made in R.O.C. They are junk! I had an issue with brake light switches on my 72'. Used parts house products. Could not get one that worked. Remember, that electronics are not returnable! After the third one that would not work, I bought a GM one at a local dealer. Less cost than the three parts house products that didn't work, and it worked fine, still does. Sometimes GM parts are cheaper in the long run than parts house products. Especially if you have to drain water to replace a part. The General has good well made parts. The first time around purchase MAY be the least expensive in the end even if initially more than parts house.

Lectric Limited seems to have good temp senders.

Thanks; I ordered one from them -- shipping was only $5.95. . .

I got the new temp. sending unit from Leteric and put it in.  The gauge still reads way too low (around 110).  When I ground the wire to the sending unit, the gauge does go to 220.  Any idea what is going on???

If the temp gauge is not pegging out when you ground the sender wire, the problem is either the gauge itself, or the wire. Might be a corroded connection at the firewall pass-thru(fuse box), or on the circuit board behind the cluster.

Did you put teflon tape on the threads of the sending unit?  Not supposed to.

Hmmm, I did put teflon tape on it.  I'll correct that this weekend.

I have used the teflon on many occasions, never seemed to bother.

If you ground the wire for the gauge and the gauge is not pegging, then it makes no difference if there is tape/sealer on the sending unit...at that point the sender is out of the equation.