Is it possible to just pressure hose the engine bay, or will I just kill the car. I am sure I will kill the car ('04 525i E60). Is there is a better way to make it look like brand new in the engine area?

 

There a was thread on m5board I think. Use scrubbing bubbles the bathroom cleaner on your bay then rinse it off. It works amazing. Then use some dressing to shine up the plastics. You won't kill your engine. Just don't drown areas like ignition coils, alternator, etc.

 

Bubbles

 

I use GUNK engine cleaner/degreaser

 

Only use products designed for automotive use. Leave the household cleaners in the house. Warm the engine for a couple of minutes. Hose the engine down with a light spray of water. I use P21s total auto wash, because its gentle but effective. Spray the P21s on the engine and scrub everything with various brushes. Hose off again with clear water. i use a leaf blower to dry the engine. I then use a plastic conditioner to give it that new car look. Don't use armor all because it will attract dirt. Check out the detailing section of this site to learn what products are available to clean your engine compartment.

I've been following this procedure after I went to a detailing clinic at Glistening Perfection. Google them for more information.