Step #1 Buy a bottle of Armor All and spray the hole bottle into your engine campartment. Note: Keep clear from the alternator and all of the belts or they will squeek, smoke and wont hardly turn!

Step #2 Then allow it to soak for a few minutes and then hose it off.

This trick helps remove grease, dirt, etc. If your engine compartment is really dirty, repeat the steps again until it looks how you want it to.

..or..

Go to your local carwash and use the No-Touch tire cleaner. Its usually a green color. It also gets at the spots that you cant with Armor All and other products and works really good! Also is a plus because sometimes armor all can make your hoses stiff and later crack reducing their life. Sometimes armor all leaves spots hear and there too.

..or..

Non-Flamable Liquid Wrench. It brakes down dirt, grease and other gunk under the hood. Let it soak for aproximately 5 minutes the hose it off.

Note: I would recommend not using any of them too much. They will all reduce the life of the paints and hoses. When it looks like it needs it or your about to sell it, go ahead. I would recommend using the No-Touch Tire Cleaner over all of them as its made for rubber parts. The Armor all will make hoses stiff and crack later in life and the Liquid Wrench can reduce paint life.