I have actually replaced the tensioner a couple months ago when I changed the belt out to a goodyear gatorbelt so I doubt it's that. Maybe air, but I've flushed it with the vacuum coolant flushing machine three times in the past eight or so months with no difference in results each time. I think I'm about down to replacing the radiator at this point. It did have the orange coolant in it when I got it so the dexcool issue seems likely. I've been using green since the first flush but maybe the damage was already done. And seeing how it even happens at highway speeds and I have tried and electric fan I don't think the fan would be the issue. The thermostat I replaced after the first episode, then it happened again so I took it back and got a second. And recently I tried replacing the 195 with a 180 so that's three different thermostats so I think that rules that out. I've bled the system for air. None came out. The brake dragging Idea, maybe but I haven't noticed and weirdness in it's coasting or sounds like they were on or abnormal brake wear.

 

Well, just to give you guys an update, ended up being the radiator. One of those cases were I went through all the cheep fixes only to find out it was the expensive one. Changed it out about two weeks ago. It's been running at the right temp ever since. Broke the sides off of the old one and it had some corrosion and brown chunky stuff toward the bottom. Probably from that dexcool the last owner had in it. So it was working but not quite well enough.

 

I had the same exact issue which is why I suggested it was a clogged radiator. In my case I'm the dumbass who mixed green coolant with the Dexcool but it was 10 years ago and before I joined the forum.

 

Does the factory come with DEXCOOL? Assume so, why is it bad to mix green with the DEXCOOL?

 

Yep, they come from the factory with Dexcool. There is a lot of info on the forum regarding the Dexcool vs green. I think everyone that is interested in this has their own opinion so I won't state mine cuz I don't want to start a battle.

 

If you mix green with orange, you get brown sludge and a clogged radiator and heater core. Never mix them! AND.....risking a battle here.....a cooling system flush will not remove 100% of the DEXCOOL so switching to green will cause the problem.

Many opinions is to replace the DEXCOOL but just follow GM instructions and replace it every five years and all should be good.