I'm having a problem with my 1640 combine overheating. Problem began when I blew a hose to the after-cooler during wheat harvest. After replacing it, the engine would overheat in about 5 minutes running at threshing speed. A friend suggested that I look for an air lock in the cooling system. Bled the line to remove any trapped air but it didn't completely resolve the issue. Now the engine will run at normal temperature at idle and up to 2/3rds full throttle. Once I increase rpms to full throttle the needle heads for red after about 10 minutes. Belts are all tight, primary air filter replaced, oil and coolant are both up to level. Thinking about replacing thermostat next to see if that helps. Any other suggestions?