Overheating during Idle only??

[CaPTuredCruiser]

My 2001 PT just recently started overheating during idle.

Never had any problems with the car running hot before this.
Temp. always remained in the middle/center of the gauge
while driving and while idle.

Replaced thermostat & coolant. Dad is a mechanic, said it was the thermostat
problem because the old one had a "shiny" scratch, apparently
that was a sign of the thermostat sticking. No problems with radiator, he said. (He won't give me any more advice what to do about the prob.)

I drove nearly 200 miles after thermostat/coolant was replaced.
No problems driving on the highway, temperature remained normal.
Could even run the air conditioning with no temp. change.

A few days later, while parking the car, and letting it idle for less than 5-6
minutes, the temp. spiked up all the way again, warning sensor came on.
Drove the car for a few minutes, temperature went back to normal.

The fan seems to be running fine, I can hear it kick on.
The temperature rises regardless of use of the a/c.

Can anyone help advise with this? Would be greatly appreciated.

[MINIHEMI46]

I'm not sure about this but from what I've read here I think you have to bleed the coolant system after everything has been changed. I think the bleeder is near the bottom of the radiator fuller neckhousing and looks a lot like a large brake bleeder valve. hope this helps

[Hooligan]

You have 2 fan speeds, one for low and one for high. Do a search on here and you will find ways to test them. Good Luck