Until recently my gay sat outside for months on end before getting any love from me . It was rained on , dusted over, craped over , and the only thing that it did to my engine bay was: 1) dirty the hell out of it and 2) make belts sqeak for the forst 20 seconds of startup. Then all good. It is a hole in your hood. Thats the bottom line. If you want a show quality engine then dont park it in the elements. If you daily your car then just accept the fact that your engine will get dirty and require more frequent cleaning. I personaly like the grundgy look of my engine bay, says its been used for what you built it for.