Discuss Balrog's answer to: we have a 98 international school bus and the ...

Here are some possibilities.  First, check to make sure the radiator is not clogged with dead bugs, road dirt, etc.  I blast mine out with compressed air every spring.  Next try a new thermostat, and have the whole cooling system drained and flushed, put in new coolant after that.  I don't know if your radiator fan has a clutch on it or not, but you need to check and make sure the fan is turning when the engine warms up.  Sometimes, if the clutch goes out, the fan will free-wheel all the time, and the engine will gradually overheat, even if you are driving at a pretty good speed and forcing air thru the radiator.  A radiator hose can soften up and partially collapse, that will also restrict coolant flow, so make sure the radiator hoses are in good shape and not soft and easily squeezed shut.  Last thing, make sure the fan belt is in good shape, and tight.  If it's slipping, the fan won't turn at the right rpm, and that can also cause gradual overheating.  I hope this helps.  Good luck