Pontiac Firebird Temperature Gauge Jumps Around - But Not Overheating

I have a 1996 Firebird, 3.8 V6 with 125,000 miles. Once it’s driven a little, the temperature gauge fluctuates rather rapidly. At a single red light the temp will fall from 240 to 170 or visa a versa. It seems to be constantly moving either up or down. Since this is my son’s car, I can’t tell if this has been going on for awhile or just started after having the radiator flushed. Any thoughts on (1) bad temp. sensor ( 2) bleeding air out of colling system (3) anything else.

Thanks for any assistance
-Donnie

Hi Donnie,

My first thought is you probably have a bad “temperature sending unit”. You can buy this inexpensive part at any auto part store and you can replace it yourself rather easily. It screws in the engine, usually on top of the manifold or on the side of the engine block and is connected with usually a single wire lead.

This is not the same as the temperature SENSOR, that is for the computer. The temperature sender sends data to the dash gauge. There is a possibility in a bad dash gauge, but that is rare, the sending unit is pretty common complaint.

Blessings,
Austin Davis