There is no thermostat; Ted took it out.

Quote Originally Posted by Ed In Mississauga View Post
Unless the engine gets up to operating temperature, there won't be much movement in the radiator as the thermostat will be closed, preventing and circulation.

As for the stop-leak stuff, it may or may not help. The principle of the stuff is that it will get forced into whatever slight gap there is when the system is under pressure. If it works for you, great! If not, I'd double check that the lip at the radiator cap is nice and level. Also double check that cap gets pulled down level when you screw it on.