I have some bare Lycoming cylinders, freshly plastic beaded. As you know the upper half is aluminum cooling fins and the lower half is steel.

Lycoming paints theirs all grey.
Continental paints theirs a silver-goldish color.
Superior paints their lower barrels black and leaves the upper portion/head bare aluminum.
Not sure what ECI does.
Not sure how much is brand/recognizability.

What does the wise man with a paint booth do?

Everywhere you look, there is a different opinion. Some say paint them black for heat to radiate out. Some say leave bare so as to not insulate. Well, the lower half is steel and will rust, I think you have to paint it. Maybe Superior is onto something.

One thing I know is that I've seen a lot of cylinders in airplanes with paint flaking off. Maybe it's the shitty factory paint job, maybe the heat is too big a force to tame.

What say?

Purely preference but I like the look of black barrels and alodined heads. These were brand new Lycoming cylinders sent to LyCon for their magic touch.

We did some testing (not airplane) for getting rid of heat in a steel object That was heated on one side and air flow on the other. The best results were obtained with a coat of black high temp BBQ paint. The black was better than raw steel in our case.The worst was a coat of high temp aluminum paint.

If you leave the porous aluminum head unpainted it will eventually end up looking dirty and oil stained. I would prep and paint both the barrel and head separately using the correct metal prep procedures and then paint separate too. It has been too many years since I painted on a regular bases to recommend a specific paint so if it were me I would go to the local automotive paint jobber and get a reeducation. Dark colors would seem best but it would probably be just fine to paint the head silver too.

Just finished painting the engine cases and sump with PPG Concept in silver. Quite the education, but such bomber paint. Is it appropriate for high heat applications too, or will it insulate too much?

My engine is painted with Concept in black, holding up well so far. We've been painting the engine cases on Kenmore's beavers with Centari for decades, never really flakes off. Centari and Concept are both acrylic enamels I believe, love both those paints.

Painted steel barrels and alodined aluminum heads in my opinion. Keep your airplane in a hangar and solvent wash the engine occasionally, engine will look good.

The composition and finish of the paint is more important than the color if heat rejection is what you are going for. Some white paint fillers have far and away the best performance (mag oxide, ti oxide). Think of all those white thingies in orbit. It isn't just fashion. White appliance paint (Sherwin Williams) can hold up to ridiculous thermal cycling on aluminum and is even better on steel (-70C to 250C, every hour and a half in LEO, 2+ years).

Matte has better results than glossy. Metallic content is generally the worst.

Stove paint will stay on longer with repeated heating. A well-known engine shop near here uses a matte black Krylon stove paint with apparently reasonable results.

After you've painted it, I would suggest spraying it liberally with a soft anti-corrosion coating. I like the CRC products. Then you can reapply it every few hundred hours, to keep the paint safe.

Seems like every engine paint job wears off, given time. The front and top of cylinders eventually starts to corrode. Mine took about 300hrs or so to start, from brand new - with two seperate coats of paint. My ECI cylinders were painted dark grey, but they were given that coat post-assembly, along with the crankcase.

Not sure if the corrosion starts under the paint or if the paint fails and moisture gets through, which then lifts the paint.... but anything you can do to stop it is worthwhile. Removing corrosion once it's there is a much tougher job.