Hello.
I just changed the thermostat on my 1991 Chevy s10 blazer. I just bought it and noticed the temp gauge did not work. The old thermostat was stuck open. My local auto parts store said the oe stat is 195 degrees. So I bought that one and put it in. Temp gauge works now. But I'll start driving and the temp will keep climbing until it reaches around 245 degrees. Then you can tell the t-stat opened and it starts falling. It will fall to about 225 and stay there for a while. Maybe 10 minutes later it will go down to 210 which is right in the middle of my gauge. Is it supposed to get that hot before going back down to normal engine temp? Maybe the gauge is off? Not sure. I'm just worried I'm damaging the engine. Maybe I should go with the 185 degree stat?
BTW the cooling system has been completely redone. New rad, temp sending units, heater core, t-stat, and water pump.

 

i dont know if this a glitch or something for these years but my 93 has been doing this since i got it and it alaways makes me nervous. it goes up to like 230 then you see the gauge drop down when the thermostat opens and then its fine.

i dont trust any gm temp gauge ive always had problems with them. maybe buy a aftermarket one just to see if it does the same thing

 

I kinda figured the gauge was a bit off. I know the fuel gauge is about an eighth of a tank off. I guess I'll get an aftermarket and see what it's really doing. Thanks for the info!

 

one stupid thing you can check is the ground wire for the gauges. had this issue on a old 83 chevy where the ground came loose and all the gauges would rear wierd, hit a few bumbs and then it would go back to normal.

basically its a small 1/4 inch screw that screws upward in the lower left bottom side of the dashboard with one wire going to it. shouldnt be that hard to find, but dont know if your truck being newer has it. ive heard of a few other people having it come loose though

 

Alright ill take a look. Im not thinking this is the problem as the volts and oil pressure are reading ok but hey ya never know.