2007 Overheating driving me crazy!!!
 

Water is radiator resivoir keeps getting hot and boiling over. I replaced the thermostat, and the resivoir cap but it kept getting hot and boiling over. The temp gauge never goes above the half way point. I finally broke down and took it to the shop. They ran a compression test and checked everything out. Said it was not the head gasket but didnt know what it was causing it. Said it could be the radiator fan, was working but said it was making a funny noise. I replaced the radiator fan this weekend and that didnt fix the problem! Im at a total loss here, if anyone has any ideas im listening..........

Debris blocking air flow through radiator? Bad water pump? It sounds as though you need a different shop.

Coolant to water ratio?
Temp the fan is coming on?
Air in the system?
Does it overheat with the AC on?

I asked if it could be the water pump, they said it was ok. Could the water pump go bad without leaking water?

50/50
I have no idea the temp the fan is coming on but I know its coming on.
How do I check for air in the system?
Yes it overheats with the AC on.

Couple of thoughts......... If my fan wasnt working is it possible the coolant getting too hot could have damaged the new thermostat? Could it be the temp sensor causing this?

I'd check to see if the rad is getting ample flow of coolant through it. Had a Blazer kind of do the same thing and it was prob 70% clogged. Take top and bottom hoses off and run a garden hose through it. It should flow pretty well with no resistance.

Air trapped in the system?>

How would I check this?

I don't know, but I read about that in the Manual...when I installed the M90, I used a vacuum fill tool for the coolant. Reference this link:

http://iihs.net/fsm/?dir=178