1992 GMC problem

[Dave L]

Hi, my name is Dave and this is my first time posting. I just found this site yesterday. I have a 1992 GMC K2500 with a 350 V8 in it which I bought new. It currently has about 73K miles on it and is in good condition. On Friday, my Check Gauges light lit up on the bottom right of the dash an the temperature gauge started moving rapidly from 180 F to it topped out at 260 F. It would stay in one position for a short time and then either rise or fall in temperature. This has never happened before. This began after driving th truck for a half hour or so. After being parked for maybe five minutes the gauge started moving rapidly after I re-started th truck. I checked under the hood and there were no signs of being overheated or any leaks. About a year ago I did have the radiator system flushed and a new thermostat put in at the dealer since I wasn't getting much heat, never a problem since until Friday. Any ideas what the problem could be? I did hear somewhere that the thermostats in GMC/Chevys of that period went bad frequently. Anyone else hear that? Could it be an electrical problem with the gauge? Bad ground or loose wire behind the dash?

For quite awhile now my RPM gauge would "bouce" up and down also when I was driving the truck in the 65-70 mph range. Could the problems be related? Thanks for any help or opinions of what could be causing the problems.

Dave L

[ChevyTech]

Hi Dave and welcome to the board.

My first guess would be that the problem with your truck is the temperature sending unit for the gauge. It should be located in the cylinder head on the surface where the spark plugs are located. Do not confuse this with the temp sending unit mounted in the intake manifold which is for the ECM (computer).

It is possible that the problem is related to the tachometer (RPM Gauge) bouncing problem you have and if so you should be looking for a bad or marginal ground connection, but my first guess is the sending unit.

Once again, welcome to the board.
Chevytech