Overheating issue at idle or when driving more than 30 min
 

I've been having a coolant overheating issue with my 2010 370z. It happens after the oil temperature gets over 180F and is worse when sitting in traffic. I took the car to z motorsports in Everett, WA where they replaced the coolant sensor, thermostat, and radiator hose. They told me that they think the problem is a blown head gasket even though the tests for that were negative and I should replace the entire motor. The car is high mileage (210K), but if it were the head gasket, it seems to me that the car would continue to overheat the more I drive it. Right now, it is the opposite in that when the coolant temperature starts to increase at idle, I just need to start driving again and the temperature will go back down to normal. To me, this almost seems like a clogged radiator or some other issue with airflow across the radiator. Has anyone else had a similar issue? Can anyone recommend reputable z specialists in the greater Seattle area? Any help would be greatly appreciated.

Are you losing coolant? What does the engine oil look like when you pull out the dip stick? Are you blowing white smoke out of the exhaust pipes?

No, not losing coolant. Oil on the dipstick looks normal and no white smoke.

Air pocket in the system. Sometimes the Z is a bitch to burp air out.