My 1991 Chevy K1500 Blazer (5.7L) has no heat, or at best luke warm. The coolant is full, I have replaced the thermostat, heater core, radiator, engine temp sensor, and the fan clutch. The engine temp stays just above the 100 mark about 120-125 or so. The blower motor blows on all speeds as it should, and I can change from defrost to floor, or blend in between and they all work as they should, but the heat stays luke warm at best. What concerns me is the engine temp does not get any higher than 120-125.

Does anyone know what the problem might be?

Thanks.

 

That would not be warming up normally. Warming up normally would be engine temps in the 200-210F range for a 195F thermostat. Are there any lines bypassing the thermostat?

 

Let me clarify myself, the Blazer starts as normal, and warms up as normal to that point…120-125 temp range. No bypasses. Everything is stock. The Blazer has a little over 80k original miles. Everything else operates fine. This problem just started one day out of the blue and I have not been able to figure it out since.

 

Is it possible that you got 2 bad thermostats in a row?

 

I guess anything is possible. I am going to check it again.

 

yeah 120 is not normal operating temperature. i had a 160 thermostat in a s10 and the heat sucked on that thing.

 

The only thing that controls the temperature in the engine is the thermostat. Something is not correct with the one you installed.