Hi everyone. I hope everyone is doing well. I wanted to pick your brains a little bit.

I have an 05 c6 base model with the LS2 6.0 with 65k miles. The car is in great shape. I just took it out of storage... ( I stored it over the winter with a half a tank of gas and some stabil... I am not sure if that will be relevant to the problem.)...When I took it out, I noticed when I let it run it would climb in temp very quickly.. reaching 190 degrees within 4-5 minutes from a 40 degree startup. It would keep climbing well past 230 degrees and keep climbing so I shut it down. I swapped the thermostat to an OE open temp (187) and the problem still persisted. Also, when I crank the heat and burp the system there would be NO heat.. just cold air.

Fast forward to yesterday, I took it for a ride to see how quickly it would heat up while driving and it almost seemed to fix itself. The heat started working and blowing hot air, and the car didnt creep past 210. I even let it sit for 10 mins just idling and still didnt pass 210.

Here is my problem. prior to this, the car would rarely ever pass 200.. even on a hot day in the summer. Now, its still heating up quickly, but not surpassing 210. I know regular operating temp is roughly 200-215 but does this sound like a problem I should still pursue? I feel like I maybe got the air out of the system from driving it but my fear is that it will heat up come the warmer months. Could this be a bad water pump that is working intermittently?

Any input would be appreciated and thank you in advance!