Hi,
If the radiator is full and the thermostat is new, it sounds like the radiator is plugged. Something is preventing coolant from circulating.
Do me a favor. When the engine is cold, open the radiator. Start the engine, heat on, and allow the engine to warm up. I'm asking because once the thermostat opens, you should be able to see the coolant moving through the system.
Try that and let me know the results. Also, you may want to consider flushing the radiator. Here is a link that shows how that's done:
https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars
Just one other thought. If the rad is clean, we "could" have a head gasket issue. If compressed air is getting into the cooling system, it could be causing an issue.
Take a look through this link and see if anything mirrors what you are experiencing:
https://www.2carpros.com/articles/head-gasket-blown-test
Let me know what you find.
Joe
Thursday, January 28th, 2021 AT 4:25 PM