What is the average temp of the blazer, is it 210? After driving for a while my car goes to 220 to 225 and can drop back to 210.

I never get the overheat light but just curious what could be going on. My coolant is full in the engine coolant reserve.

 

The thermostat is supposed to open at 195. Don't expect the in-dash gauge to be perfectly accurate..... 200 is prolly about right.

 

What does your coolant look like??? Does it look dirty at all?? I would do a cooling system flush and replace the thermostat if I was running hot!!!

 

What year is your blazer?

 

If the temperature starts to climb then abruptly lowers, that would indicate you are low on coolant..the rise would be caused by an air bubble in the system and the fall is when coolant gets to the sensor. Check your coolant levels (and cap while you're at it) and if that isn't the problem, a thermostat sounds right.