In Reply to: Aluminum engine parts discoloration? posted by Matt on August 07, 2001 at 14:29:37:
The dealers are supposed to remove the cosmoline coating as part of the dealer prep -- but they rarely, if ever do so.
If left on, after a while, the cosmoline coating just bakes on as that yellow-brown crusty residue.
The only way to remove it chemically is to use a strong solvent like a paint stripper. You may find some references to posts by various people who have done it this way. Strippers are really bad for you, and you need to use them in a well-ventilated area. They also are very dangerous to all of the non-metallic parts in your car -- so you have to be ultra-careful in applying it.
The best solution I've seen is having the parts bead-blasted . . . pretty much like sand-blasting. You can remove the parts you want "cleaned" and put them in a bead-blasting cabinet. Many shops have them.
Or, like most people, you can forget about it and live with the slightly ugly color.
Here's a topic I've not seen come up. In my own M30 engine, and in many other Bimmers I've seen pictured online, the engine's large alloy pieces (valve covers, intake runners, etc.) often seem to have an amber colored discoloration all over them. Is this common? If so, what is it and how does one remove it?