You can take it down to one of those coin-wash places with the power sprayer; or, if you've got your own pressure washer, you can do it in your driveway (but you'll have to clean up a pile of mud later)

What I do first is open up the hood and blast the underside of the hood real good. Then I move on to what surrounds the engine--as much of the firewall as I can get, fender edges and aprons, moving forward to the radiator supports, back of the headlamps and surrounding area, washer bottle, etc.

I'll spray off the engine in real quick bursts. Usually the front of those 3.8's are caked so I try to get it real good.

DO NOT directly powerwash:
a. The alternator
b. Idler pulleys
c. Fuse box
d. Air box inlet
e. Coil packs
f. Computers.

You can spray them lightly but don't aim the wand directly at them.

I also get down on my knees in front and spray out the grille and stuff stuck in the radiator. Then I spray under at the diff, suspension components, underside of the engine, driveshafts.

Once I've knocked all the heavy crud off, then I get my spray bottle of Simple Green (full strength) on just about everything...engine bay, underside of the hood, fender wells, visible undercarriage. For the engine bay, I'll take my "not for the exterior" wash mitt and with a little dish soap, get the underside of the hood, edges of the fenders, all the big visible stuff and plastics but not on the engine itself.

Rinse with the power-washer. Rinse like you've never rinsed before. This is between you and your Jeep, man, but stick that wand where the sun don't shine and get everything.

Once everything is nice and soaked, I'll let the hood down (but not buckle it as a reminder I have more work under there). This is where I fill up a bucket of nice soapy water. I'll rinse down the body again with the PW, hitting every crack until mud no longer comes out. Then, I use a mitt to wash everything on the outside real nice. I open up the doors and get the jambs real good.

Rinse the exterior. Then dry. I'll do a quick visual check for any damage incurred that may have been hidden by mud.

Open up that hood again. If you've got an air compressor and air chuck (or even a good electric leaf blower), blow all that water down to the ground. Then, I'll take a towel and get the underside of the hood, edges of the fenders, anywhere there's standing water.

The next piece is important. Buckle everything up. Start the motor, and go for a drive. What you DON'T want is water to steam and pool under the hood. If you just wash and then shut the hood, everything in there gets SUPER humid and that's not good for the electronics. So a good drive will boil everything out, warm everything up, and the air will dry everything out.

Once I'm home I'll do a quick visual check under-hood again, check all the fluids, wipe down all the door seals, hood seals.

Once you do this a few times and work on your technique, you'll be able to take any JK dipped in mud and be able to make it look showroom-new. The key is to go SLOW. Newbs with the loud pressure washer and squirting water always want to work fast and move that wand around like it's hot. SLOW down.

I wear eye and ear protection because I'm standing next to that PW for a good 30 minutes while I do this. And, I'm usually wearing more mud and have more on my face than the Jeep started with. Go figure.

 

I've never been a fan of pressure washing the engine. It's really not necessary.

Whenever I've cleaned my engine/engine bay I've always used plain old car wash; a garden hose on the mist setting, and a toothbrush. Here's the engine by I cleaned up on my fiancé's Dodge Avenger last fall. After I cleaned it I followed it up with some 303 Protectant on all the plastic and rubber.

 

I blast mine furiously with my pressure with not a care in the world.... I do although half ass try and avoid the cold air intake... So far so good...

 

This sound like my thinking when it come to my vehicles.

 

Bump for any other thoughts on cleaning the engine bay. Good thread so far.

My Pentastar is getting awfully dusty and grimy so I need to clean it before too long. I stear clear of mud where possible so I'm not dealing with that.

 

I spray down the entire engine and component so with simple free, let it set for about 5-10 minutes (not letting to dry), take a soft long bristle brush and gently wash, then rinse with a garden hose, and yes, rinse everything. A little fact not so widely known, cars electrical systems are tested for water submersion and must workfare a given number of minutes. Getting things wet, doesn't hurt it. I've been doing this for two decades. My S60 Volvo, got it every month or so for 10 years, no problems. The simple green is my choice as it doesn't cause putting, spots, etc if you leave some residue behind. And it's biodegradable.