Originally Posted By: UltrafanUK
Originally Posted By: Jetronic
Originally Posted By: dparm
Paulri, your car isn't oil-cooled, it's water-cooled.
Yes, the oil will help dissipate some of the engine's heat, but it's not huge.
but the amount of heat generated by the shearing of the oil can be huge...
Must be a joke, as it's only true just as an engine runs out of oil and goes boink.
Nah, it's not a joke.
The amount of heat generated inside an engine due to the shearing of the oil film is of the order of whole KW, and a few of them.
For example, the oil film in the big end is going to be some tens of degrees C hotter than the big end, which is some tens of degrees hotter than the oil supply temperature...due to the shearing action in the oil film.
Rather than "carrying away" heat, they are generating their own heat, heat that then gets carried away by the oil flying out, or conducted from the big end to the main, and to the coolant.
Piston skirts waste significant amounts of energy, straight into the coolant basically...OTR designers are looking at thermal barrier coatings to run the liners hotter mid stroke and thin the oil out locally.
The economy benefits of thinner oil are due to less wasted energy...energy that is turned into heat. If there's a reduction in temperature, it's because of this reduction in frictional heating, not because thinner oil "flows" and caries heat away as many think.