I can't find any leaks. The overflow tank is at a normal level. Radiator is full. Heater blows hot. Fans work with A/C on. My car was in the shade all day. I stepped out to run to the store and left the car running while I was inside( for 5 minutes). Come back out to the car and it's overheating. The car also sounded like it was idling up and down. I jumped in and threw on the heater and within a few minutes the temp went back to normal. The same thing happend to me a few weeks ago. I thought maybe some air pockets, so I tried to follow the purge procedure. I also did a search for overheating issues but couldn't find a match to my issue.

 

do the fans work when the AC is not on?

 

Yes fans are on with A/C off.

 

still sounds likea michael buble in your fluid.
air pocket indeed. dunno...