Oil that doesn't burn, but does get hot and then gets thrown away would have a significant cooling effect. That is a good reason for Castor Oil. It gets VERY hot before it burns and all of that heat is passed out of the exhaust. Rich mixture does pretty much the same thing. I had a friend who flew P-51s in WW-II. He took a hit to his cooling system that caused a total loss of coolant. He flew all the way back to England by pumping extra fuel into the engine with the primer making it VERY rich, but not so much as to kill the engine or set the plane on fire. He said his palm was an open wound where his flight glove wore through by the time he landed and the engine was shot, but it never stopped and he brought it home, with NO COOLANT in the normal system. Half way home I think he was more worried about running out of fuel than engine failure.