Join Date: May 2019
iS-10 till 12 is offline
Re: 89 Chevy S10 Overheating
Run a $20 coolant temp gauge. Can even zip tie it under the hood (mechanical but keep it away from the header, fan, steering, etc.) or run it into the cabin. Go drive it. Let the engine get to temp, but go off the new gauge. My 2.8L hangs out around 190-195 when it had the mechanical fan and now electric fan.
If the temps stay in range but the dash temp is going wonky, it's electrical. I'm running into a minor electrical issue on mine, that's seemingly related to the 14 gauge charge wire off the alternator running back in the loom (dunno wtf they were thinking running a tiny wire like that even on low amperage, and it doesn't even directly go to the battery). In my case, I noticed the passenger headlight was dim and the heater motor is intermittent, so I'll need to look at the wiring.
Dunno what '89 was like compared to my '82, but if it is electrical, it might have fooled the PO into thinking it had overheating issues and might be easy for you to fix.
The biggest thief is time.