Temp gauge overheating

[ElLoboSolo]

Hi there,

I have a 2007 Pontiac Torrent 3.4 L that has 201,000 miles. Had it for about a few months; Changed the water pump, starter, a few pulleys, new battery and wires, serpentine belt, ect. Been driving well until two days ago when my car started overheating on the highway while I was pushing 70 mph. Temp gauge kept fluctuating as I increased and decreased RPMS but, finally red-lined and reduced power to my engine forcing me to pull over and let the engine cool. An error message on the dash reads "hot engine, no A/C" and "Idle engine, reduce power" I've disconnected the battery and let it sit for a good half hour, gone on a test drive and it'll do fine for about an hour or if I'm doing higher speeds on the highway. I've checked the thermostat again, made sure their were no air bubbles in the lines, and honestly I don't know what else to. Does anyone have any ideas ot has anyone dealt with this problem before? Any help provided would be greatly appreciated, thanks!

 

[melsg5]

how did you check the thermostat, removed it and placed it in a pot of boiling water to see if it would fully open?
have you done a hydrocarbon test on the coolant, auto parts stores sell a kit?
have you pressure tested the cooling system including the cap?
do the engine fans come on when you turn on the AC?
do the engine fans come on when it is running hot?