My temperature gauge isnt working. I put a new temp sending unit in, still isnt working. I ground the gauge wire out against the engine and the gauge pegged out. Seems the guage is working. What could be the problem?

 

When you installed the new sender did you put teflon tape around the threads. If so, the sender is not making contact with the metal in the block. Take the sender out of the car and wrap only the very top threads. Then reinstall it in the car.

Grounding the gauge out and getting a full hot reading indicates the gauge is working.

You can test the sender with a ohms meter. A cold sender will read right around 600 or more ohms. A hot one around 50 to 75 ohms. The wells TU5 sender is about the most correct sender available today for the early modle cars. Since I don't know the year of the car I don't know the sender we are dealing with or if it is one wire or two. I am posting an email that I received from Noland Adams in regards to the tefflon tape and sending units. I hopes this help you resolve the problem.

Email by Noland Adams:

The temperature gauge circuit counts on a variable electrical value to measure
temperature. All 1956 to 1967 temperature systems use a single post
temperature sending unit; I believe the first two post sending unit was used
in 1968. Installation of the sending unit is important, here's why:

In order to complete the 1956 to '67 temperature sensing circuit, the sending
unit must be firmly seated in its mount in the intake manifold. If you wrap
the tapered threads with too much teflon tape, you could partially insulate
the sending unit's pipe threads, producing an extra resistance, which would
cause errors in the temperature reading. The real reason for pipe dope or
teflon tape on the sending unit's tapered pipe threads is lubrication. Use
just enough to allow the tapered pipe threads to slide against each other
until the sending unit is firmly installed in the manifold. If you do not use
enough lubricant on the pipe threads, they can gall, and roll little metal
pieces into the threads. Galling prevents the tapered threads from sealing
against each other, and the fitting can seep. It's usually not a big leak, but
it is an annoyance.

I suspect many incorrect cooling temperature readings can be traced to a poor
electrical connection at the sending unit's threads. I hope this helps.

 

The threads were all covered with teflon tape. I removed all the tape except the last 2 threads. I hope that works. Oh yeah, the car is a 69, only one wire. Thanks