Ok, I have been racking by brain over this. Changed my thermostat a few months ago and ever since I can't get the engine up to normal operating temp unless the ac is on. Shortly after it gets there, it starts to get too hot....
I have tried burping the system several times, without the ac it stays cold, with it on it overheats. Fan clutch is a suspect, as well as the tstat being faulty considering I used a "failsafe" before I found out blazers do not like them. Anyone else ever experience this issue!? Ive never had a problem with both too cold and too hot at the same time. So confused that i dont even know where to start.

 

Not trying to insult you, but you did put the thermostat in right side up, right?

 

I'm pretty sure it's in there correctly. Unless the one I removed was in wrong....ive changed quite a few tstats and never thought about the person before me working on the vehicle.

 

The spring should be on the bottom. If you aren't sure, you might want to drain the coolant, pull off the upper hose, and check.

 

I plan on working on it today. Checked coolant the other day and the system really needs a flush. There is a good bit of what appears to be rust in it.