UPDATE - I wanted to wait a bit until I drove a while to report. So, the car stopped overheating???
The only changes that have been made is I did replace the aftermarket thermostat with the actual dealer thermostat and since I have been testing I have been running on water only.

It runs great at about 199 to 219 typically. Seems that the fan once kicks on at 216 stabilizes the temps. I'm more worried now that it's driving perfect and not overheating without a resolution as to why it was overheating.

I have been checking the water levels before taking it out each time and it's always right where it is supposed to be. The reservoir is full and no indication of overheating any longer.

I took it out day before yesterday and got caught in a long traffic jam then proceeded to drive around 60 miles round-trip car maxed out at 221 in traffic then dropped down to 205 on the freeway.

Not sure how to explain this but I'm concerned about draining the water and replacing it with Dex-cool at this point.

GO FIGURE???

 

I believe it was the incorrect thermostat.

 

It is running a bit high now, DexCool might bring that down.

Maybe somebody decided to put a cardboard gasket in the t-stat and there is a bit floating around obstructing the flow. Or installed the rubber o-ring wrong.

 

I had installed 2 aftermarket thermostat before installing this ac Delco thermostat. I actually tested the original with the 2 newly purchased thermostats and all opened perfectly at 160. But none seemed to work when installed in the car.

This dealer thermostat finally seems to do what it is supposed to do. Only thing I can think is different is this thermostat. All were installed properly and the system was flushed between each installation.

Still unsure about installing the Dex-cool, why fix what is not broken??

Just saying.

 

I hope that was a typo! Should be 180F.

Do what you want, but DexCool does more than keep it from freezing. It also keeps it cooler and reacts to tiny leaks and lubricates the water pump. It would not be a smart move. Just saying.

Possibly the t-stats interfered with the housing so did not open.

 

Yes, you're right 180.

 

I'll replace the water with Dex-cool but I'm pointing fingers if I'm overheating again...lol.

 

50/50 Dexcool

 

Running straight water without coolant would cause overheating and boil over by itself. You're lucky you are messing with a pretty stout drivetrain. I just read through the updates since I posted and cringed at it. Are you trying to kill the car? Run the correct thermostat and get a proper 50/50 mix of dexcool in there.

 

Using straight water is the most effective coolant to remove heat from the engine. Using a mix does a couple of things. Corrosion prevention and freezing are the two main factors.
Try using straight anti-freeze (not a 50/50 mix) in an engine and see what happens.
Overheat issues can be made as simply a bad radiator cap that doesn't keep the boiling point of the coolant in check. Every PSI the cap can hold back "lowers" the boiling point by 3 degrees. So a 21 lb. cap can let the water get to 63 degrees over the boiling point of water at 212*F, which is 275*F.