[QUOTE="Tegger"] They corrode wherever exposed metal is (steel, iron or aluminum). In a North-eastern climate you will get LOTS of corrosion on a clean engine. It'a actually better in those cases to leave oily grime on to prevent corrosion, especially on electrical connectors and bare aluminum. My engine bay has been treated with the "drippy" rustproofing every year since new. It's a horrible mess and filthy to work on, but there's zero corrosion wherever the oily film has managed to stick. It's that fact which prevents me from getting the engine bay cleaned, as much as I'd like a clean engine bay.[/QUOTE] I saw some corrosion on the aluminium alloys after using tire cleaner once. This green stuff. Not from soap and water. But corrosion in this case is just discoloration of the surface and not peeling off rust, like you have with the iron...