Erratic temp guage

[gbhrps]

Gentlemen,
My 55 was totally restored 2 years ago and for the last 2 seasons the temp guage has worked well and fairly accurately, rarely going above the half way mark. Fresh out of winter storage with about 150 miles on it this year, I find that the guage is all over the place. A check of coolant levels, tight fanbelt, a a good connection on the temp sending unit finds no problems there. The guage reads about half a needle's width just right of centre most of the time now, but will climb to the three quarter or slightly higher mark in slow traffic, or at idle at a light. Strangely as well, when starting with a cold engine, the guage will not bottom out by going full left on the guage and rising from there, but rather starts right at the dead centre mark or slightly less. Is this an indication of a sending unit that is going south, or should I be looking somewhere else?

 

[gbhrps]

Removed the temp sending unit and cleaned it up. Put an OHM metre on it and placed it in a pan of water on the stove and turned up the heat. Starting at 15.1 ohms it went up a few tenths, and then jumped to 23.7 and quickly down to 15.5. It continued this up and down going all the way up to 122.8 ohms and immediately down to 36.1 in a flash. After the test I discovered that the electrical terminal was loose on the top. Its rivet was slightly loose. I put it in a vice, and using a drift and a small hammer, I peened the rivet back down. When put back into the car, I found that the guage is now performing as it was intended. Although the reading is about in the middle of the M in "TEMP" (a little on the high side) on the guage (Its 92 degrees F here today) it appears to be finally operating fine.