Also, in addition to my mention of coolant mixture, a acidic/corrosive coolant will eventually lead to an overheating situation as well. I mentioned a eaten impeller. I have seen this a few times in my years in the trade. The impeller is so eaten away there is no coolant flow.
One was so eaten, heater core was blocked, head gaskets eaten away, aluminum heads could not be shaved so dimpled they were from the acidity. This van was in such bad shape, client decided to just buy another one.
I do remember high mileage on it, and no doubt in my mind the coolant had never been changed in the 15-20yrs it had been on this planet.
And since we are on the subject, coolant electrolysis is also a factor of corrosion which also will lead to an eventual over heat situation. Often times, this inside of the cooling system will eat itself away and block a radiator or core, eat away at heads etc. You can actually measure that with a voltmeter. Anything over 0.3v means the coolant is in electrolysis and needs to be changed.
Ok, I am on a roll, in diesel engines, there is also a phenomenon called cavitation. This causes overheating by eating away at the liners causing thin wall and transfer of heat to the coolant, or so this is how it was explained to me.
