I don't clean my engine bay too often because it's pretty clean already. I read something on here that someone used a foaming tire shine to clean hoses and plastics. Just don't let it sit too long... probably best to do that at a car wash where you can use the degreaser and pressure washer. I don't know if silicone spray would be a must in there but I suppose it could keep things from drying out. Just avoid saturating the alternator and electrical components with too much water.