+1. This is what I use. Have had no problems. My '06 mustang had 18k on the clock and engine was spotless by doing this, and not even once a week.

 

+1 on the psi washer;at work thedetail dept hit a charger r/t's engine bay with one during a full detail and wiped out the front control module and underhood power dist. center (luckily still under warranty)...

 

I normally just soap up the areas I want to clean with a sponge avoiding the battery, fuse box and obviously the filter. I then spay the engine down with the garden hose on a low pressure. When I am finished I use my leaf blower to get all excess water off the engine. The rest I dry by hand. Hitting the engine with just the leaf blower once a week will also help keep the dust and dirt off your engine without even needing the hose. This seems to have always worked good on all my cars. Here's a look at the results from another one of my posts.

 

Personally, I drive it up to the local Ford dealership and have them do an "engine bay clean", my guy does it in 5 minutes and for free, I tip him of course. He covers the fuse box, battery and air filter and than sprays it all out with water. This CAN be done while the engine is warm, but I wouldn't suggest it doing it after a long hard run until it cools off.

Look at it this way - if they screw it up at Ford, who pays for the repairs? FORD. That's how I like it and that is why pretty much everytime I touch my car I touch it at a Ford dealership. They are responseable for what they do on their lot on their time.

Either way, it isn't that hard and if you do it right you will be fine.