| purging air out coolant system
I am not sure if your engine has a bleeder valve at its highest point, some times you have to jackup the front of the car high up purge the system. cannot stress how important to get all the air out! 2. after this process and if condition still exist! 2. if it was a water pump or stuck thermosatic it would over heat in within a few mins. 3. coolant sensor/ fan switch is mounted high up on the enigne where the air pocket is it would never come on. reason to make sure all air is purged out. | 
