94' Blazer Temp Gauge Jumping Around

Hi my blazer started overheating one day, so I changed the thermostat, for one week it would not warm up past 120, now the gauge even after 15 seconds of running will bounce up and down real fast from top to bottom from bottom to middle and all over the place . Does enyone have any idea what is going on here ? thank you for the help

Possible bad temp gauge sensor/switch.

Coolant temperature sender is bad or the wiring has a short.

Should be the sensor near the middle plug on the driver's side of the engine.

Coolant temperature sender is bad or the wiring has a short.

Should be the sensor near the middle plug on the driver's side of the engine.

Ah, what is the proper term? the parts box says switch when I replaced mine.


And the temp sender/switch/sensor/probe is on the passenger side on my 92 4.3.