This may be a little off topic..but this subject remends me of a whole series of tests that were done on engine color (cylinder & head color particularly)..back in the early 1960's..when most motorcycle engines were air-cooled..and temperatures/overheating was a continual concern.
The bike I was riding in particular..an Ariel Square Four..tended to have overheating issues with the two rear cylinders..tucked behind the front ones. Factory engine color on those bikes was silver/aluminum..but they found that by painting the cylinders..sometimes the heads..BLACK..that the running temps were reduced by 10 to 15 degrees F. That was enough to remedy the pre-ignition problems with the two rear cylinders on those bikes.
I remember also..that other bikers would paint their heads and cylinders darker colors..to have the engines run a little cooler (this was in So. California..in the Summer..where ambient temps were well over 100 F.) If I remember correctly..the reason the darker colors ran/run cooler..is that it allows for faster heat dissipation to the surrounding environment.
Nowadays..with oil/liquid cooled engines..I guess this isn't so much of a concern..but it still seems useful to know..for these old Honda air-cooled engines.
Ichi
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The same thread
http://forums.sohc4.net/index.php?topic=58519.msg633944#msg633944 after Mark's post also goes on to say that painting cylinders darker colors helps REDUCE over-heating in the air cooled engines.
Think it's probably good to differentiate between heat build-up and heat transfer. As Mark indicates..the heat internally may be greater on average (as evidenced by the higher oil temps)..but the overall heat dissipation seems to be more uniform from darker engine/cylinder colors.
As mentioned above: the external cylinder temps/readings we were getting (not oil temps mind you) were running 10 to 15 degrees COOLER on the rear cylinders than with bare aluminum. As another example: with the old iron cylinder engines (Triumph..Ariel..Beezer..Harley..pre 1960's..for the Brit bikes. It took Harley another 20 years to start using aluminum/sleeved cylinders)..they were always painted black..for better/more uniform heat dissipation.
But again..nowadays..with oil and liquid cooled bike engines predominating..this topic probably doesn't attract such scrutiny.
Ichi
