There maybe some antifreeze getting into the cylinder while the engine isn't running and gets blown out at startup and while the engine is running the 120lbs of compression is pushing air into the cooling system. U dont alwsys see white smoke.

 

Well there is a down stroke. But okay that info is good to know. Learn something new every day.

 

Hi, I know this is an old post. What turned out to be the problem here? Did you get it fixed? I’m asking because the exact thing just happened to my 08 jeep wrangler. And I do mean the exact same lol, the replaced water pump and thermo and the radiator exploding. Can you please lmk what became of your situation? Thank you