Motor: To paint, or not to paint?

So I had an argument with a friend of mine tonight over painting air cooled motors..
I have built several of off road machines, 2 & 4 stroke. I've painted many of the motors. But nothing to this caliber!
His argument is that these 4 cylinders hold way more heat that single or 2 cylinder motors, and the paint will disrupt airflow over the cooling fins.
I call BS! I was thinking of painting just a few parts with a few thin coats of low gloss black engine paint.
In my theory the black paint should help disperse the heat.

Anyone have some actual scientific input on this?? Cause I think he's full of sh*t.. lol

 

5 of the bikes in the showcase have painted engines. Science!
http://www.xjbikes.com/forums/showcase/

 

The midnight maxims came painted black from the factory, so I would think that it isn't going to hurt much. If anything, they might run a very tiny amount hotter because of the black paint absorbing light, but that isn't going to disrupt airflow over the fins. Anyway, I believe most of the engines were at last partially painted, I think the top half of the cases and cylinder blocks have a silver paint on them.

 

Nothing wrong with painting an engine, most of our XJ engines are painted from the factory. They say that black paint makes an engine run cooler, it dissipates the heat better. Look it up , there are many articles on the subject.

 

We'll that was my theory to.
I'm gonna paint it anyway, and polish up some of the shiny parts.
I have an aftermarket oil cooler to, so I'm not really worried.

 

Tell your friend that four cylinder engines also have more surface area to dissipate heat from.

 

I believe his theory had a bit of merit. I could see if it was polished, a high gloss paint, or even clear coated. The smooth surface might disrupt airflow over the cooling fins?
But the paint in my mind shouldn't hold enuf heat to hurt it..

 

His theory does have merit, and in fact it is true that coated surfaces dissipate heat more slowly than uncoated surfaces (there are exceptions). There is a huge caveat however. The percentage of change is teeny-tiny; so small that it's insignificant. It takes many coats of paint for the insulation to raise engine temps enough to cause longevity issues, and a whole-lot before it will cause damage.

I wonder if he ever looked at the radiator of a water-cooled engine. The vast majority are painted.

 

I painted mine with VHT Engine Metallic - Black Pearl and I really like it - also did seem to make it run cooler and I've not had any issues.