I have had a few inquiries as to how we went about painting the engine and the aluminum parts like the radiator.
With the radiator and aluminum parts we typically send out the part to be powder coated with some kind of primer. This way they blast the tanks or aluminum parts and then coat the aluminum parts with a primer that is baked on. We have found this to work the best. The obviously don't blast the fins of those come back still clean. But you can do the surround and the tanks on things like radiators, and AC condensors. We also do it on anything smooth that is aluminum as we feel the "BITE" of the primer is better with the blasting and heat for the part with primer. We then stack any needed body work on top. Here are some parts we had blasted and primed that I have pictures of.
Here it is with body work on a 2nd coat of epoxy primer. We are letting the body fill dry before sanding.
You can see the top billet aluminum piece in primer. We really shouldn't have any body work on a billet part.
Now the unpainted fins of the Condensor or Radiator in this project will get sprayed with Krylon to keep the cooling capacity to the highest level with the thickest paint. I had a guy at a radiator shop once tell me they cool better in black spray paint, not sure I believe him. But there is nothing worse then seeing aluminum fins through the grille opening of a car.
Now the engine and manifold parts go through the long deburring process. They are then shot in epoxy primer. The primer is given a good couple days to fully dry and since we are not body working the engine we shoot a minimum coat of sealer and the regular base coat clear. And really just enough to cover the engine.
I help that answers your questions.