Oil is a vital component is cooling engines. When I was buildings RV's (Matilda Motorhomes for the Ozzies) we always put oil coolers on the transmissions and engines. And on that subject as a poor (financially) apprentice I once used 100w Shell aero oil (for P&W round engines) in my Ford Zephyr. Marginal in summer but locked the engine up solid in winter in Victoria. Such were the variations in air temperature. One of my apprentices having seen me use Mobil Jet 11 in a car engine just before stripping it tried the same trick but continued to drive it with top ups. The cleanest seized engine I have ever seen. And Dave I still won't use castor in my 4 stroke glos but I am using it up in the diesels (including the Enya 41 fourstroke)