Clean engine

Avoid getting the engine valve cover wet since water can easily drip down past the four spark igniters into the spark plug wells and cause engine misfire.

Other than that, it is OK to clean the engine using the least amount of water possible, to avoid getting water into the electrical wiring harness connections. After you have finished cleaning, you should take the car for a drive so that the water in the engine compartment will evaporate.

 

Why do you need to wash the engine? Can you not just wipe the engine down with a wet cloth? Use a small brush (like a toothbrush) to get into the small areas where a cloth will not fit. This is much safer than washing with water, and you'll get better results.

 

Last week we witnessed a Gen2 Prius come through the shop that had a full detail prior to going to a car lot. The detail facility did spray the engine compartment and apply tire shin to hoses etc... Looked great but the prius showed up in our service drive with missfire codes for 2 cylinders as stated above.
A better way to do this would have been to use a parts cleaner areosol that can be found at an auto parts facility to remove grease, oil if thats your concern. For example if you had a seeping valve cover gasket you should get it fixed but parts cleaner spray would clean that up. Otherwise to make it look nice you should be able to wipe down most visible components.
Obviously you need to educate yourself about what you can and cannot touch safley under the hood if you want to take this approach.

Another thought, and possibly the easiest way would be to ask your trusty service center to clean up under the hood at your next service interval... We would if someone asked us to.

 

Pledge Furniture polish in a aerosol can does a nice job on light duty cleanups. The silicone in it leave rubber parts shiny and pretty. Just spray it on and wipe it off, use a brush to get into tight areas.

 

I like to detail the engine compartment every 4 months or so, depends on the winter rain cycle. No sense cleaning, only to drive through crap the next day.
I use a clean rag, wipe off the light coating of dirt , now is the time to look for leaks, cracks, things that do not look right, wipe down the fluid bottles, check their levels, top off if necessary. I pull the air filter cover, pop out the filter, tap it to remove any loose debris. Shine a flashlight down the throat, take a peek. While the cover is off, it makes for a little easier ability to reach in and wipe down. So far, in all the times I have done this, I have found no problems, but was satisfied there are no potential problems throwing clues I would not have caught had I not done the cleaning!