[oxfordsteve]

I like the idea of making it simple. My collegue next door tells her 9th grade physical science students that conduction of heat occurs between materials in direct contact with each other while convection of heat occurs through air flowing around the object and radiation occurs when an object transfers energy across space to another object.

My field of expertise is Biology so I will not pretend to be an expert on physics and I certainly do not know as much about thermal transfer as some members do. Sometimes physics seems to defy common sense but here is my tiny bit of common sense with my small amount of physical science knowledge:

Engine conducts majority of heat transfer to coolant through conduction, most of the little left through convection due to airflow around. Radiation only becomes significant after engine is shut off and sits there with no coolant flow or airflow. In that case if it was considered a "perfect black body" then it might be a slightly better emitter than other colors while transferring heat. (I have serious doubts about the black body status as a coat of rustoleum may not qualify it but I yield due to lack of specific expertise in that area.)

I just don't see that any radiation from the surface of the block significantly affects cooling compared to say flow of coolant regardless of color.

If I am wrong I am sorry, I am not speaking as an expert, just offering an opinion. I am open minded if someone can offer definitive proof otherwise.