We detail the engine compartment on every front hit we repair. Use 409, mean green or some such extra strength detergent. With the engine cold, and taking care to avoid the fuse box ( and intake filter-if it has a distributor, wrap it in plastic or foil or just stay away from it) spray everything with the soap. Greasy areas may take more than one shot. Let it sit a few moments, then rinse it all down using a gentle spray from the hose. We've done a few thousand cars this way over the years and never damaged any. Wayne