Recommended tools to clean an engine compartment (like this 2007 Audi A4 Avant). First, P21S Total Auto Wash. A great cleaner for the dirt and grime that accumulate on the plastic, rubber, and metal surfaces in the engine bay. autoobsessed.com/products/p21s-total-auto-wash-1000ml-wsprayer
If you need a little more power to clean oil or grease, try Nextzett's W99 All-Purpose Degreaser. autoobsessed.com/products/nextzett-w99-all-purpose-degreaser-concentrate-1-liter Good brushes are key to doing a good job in the engine bay.
Wheel Woolies 9-inch Boar's Hair Brush is good for flat surfaces autoobsessed.com/products/wheel-woolies-wheel-fender-premium-boars-hair-brush-9-inch
Wheel Woolies 3-piece Kit is great for getting into narrow areas autoobsessed.com/products/wheel-woolies-obssssd-series-3-piece-kit