Engine detailing is not the mystery that people like to make it out to be. There are a few areas that you want to avoid, but other than that it is pretty easy. Here are some areas outlined on a 2005 Subaru Legacy GT engine.
A: The air filter doesn't necessarily have to be avoided unless it is exposed. In the case of a short ram intake or a full length CAI you will want to keep the filter as dry as possible. This may include covering it with a pastiic bag, but just make sure you take the bag off again before you start the car.
B: This is the intercooler on the Legacy GT. Certian vehicles with top mounted intercoolers should have care taken around this area. The fins can be bent by high pressure and you don't want to be scrubbing them too hard with anything else that might bend them either. This is also an area for many other four cylinder vehicles that will allow water to get into the spark plugs. You'll find it difficult to start the engine if that happens, so try to avoid getting the top of the valve cover wet if there are four spark plug wires going into it. Examples of that can be seen in the photos section on the tabs at the top of this page.
C: That is what the alternator looks like. It is a cage looking thing with copper wires wrapped around inside it. You most certianly do not want to get anything flamable or combustible inside that. Especailly if it is hot. I've seen an alternator catch fire 30 minutes after the car was stopped because someone sprayed degreaser on it. Avoid spraying it with anything. You can shield it with a bag or even just a towel. Sometimes there are hoses and other things nearby that you want to spray, so just be careful and shield it whenever that is the case.
D: Avoid spraying the battery directly since that is an electrical connection. That other part above the battery is a fuese box in the Legacy GT engine bay. Most cars have something like that in there, so avoid those too. Would you spray water in the circuit breaker box in your house? I didn't think so. Don't spray them in your car either.
So that is pretty much what you want to avoid. Never approach engine detailing like you are putting a fire out anyway. Just remember that next to your paint (which your car can still drive without) your engine is the most expensive and definitely the most important part of your car. Don't risk screwing it up just because you want to take as little time as possible in cleaning it. Take your time on it once and then you can just blow through it every couple weeks or months after that. I'll be honest... I detail the engine of my Pilot every four or five months. Even then it isn't really much of a detail. I just spray some degreaser around the edge and rinse it off. Then I dry it and spray some CD2 Engine Detailer on it and walk away. A couple days later I might pop it to wipe it down again, but it is a five minute job every few weeks to keep that thing maintained.
Ok, so let's get down to the process of how you get it done.
First of all, and make no mistake about this, THE ENGINE MUST BE COOL! I won't be held responsible when you toss cold water on your motor after driving for two hours in the summer heat and having your block crack. I'm telling you know that the physics of hot and cold are not something you want to mess with. The best time for an engine detail is two or three hours after your car stopped running. I do my engine details in the morning before I go anywhere. For my customers if an engine detail is part of the job then I go to them and advise them to leave the car parked until I get there. If they must bring it to me then I tell them that I have to let the car sit for an hour with the hood up before I touch the engine and it might slow down my process a bit. I'm just not going to take any chances with damaging a hundred thousand dollar car's motor. Shoot, I'm not risking damaging my fifteen thousand dollar car's motor, so you can bet that I'm not going to take chances with yours either.
My degreaser of choice is Gunk Foaming Engine Degreaser. I like it because I can tell where I sprayed it and it sits on the grime a little longer than other types. I've used lots of other types and they all pretty much work the same, but given a choice I'll pick one that foams. It is probably just a personal thing, but this one doesn't smell as bad as some others and it just seems to be easiest for me to use. Anyway, I spray this product around the engine bay while avoiding the areas we have already talked about. I generally don't bother spraying the valve cover with it since that is going to either cause degreaser to drip somewhere I don't want it, or because that is an area I generally prefer to wash by hand. However you decide to do it, just remember to avoid getting it in the spark plugs or the alternator.
Don't let the degreaser sit too long. If it dries (which it will do in a hurry) then it can stain. You want to rinse it off as fast as you can put the can down and pick up the hose. Just use low pressure and your thumb to adjust the force of the stream. For the most part you just want to rinse the degreaser off, but there may be some spots where a little blast is appropriate. Rinse all the way around the engine and don't forget to flood the pools that collect near the fenders. Look down in the sides by the fenders and make sure there isn't any grimy water anywhere.
After you have rinsed off all of the degreaser you can go in with brushes and towels. For the most part I like to just use a couple microfiber towels and some diluted all purpose cleaner. The trick is to get your towel near the grime. For that you'll need some nifty tools. There are those cheap detailing brushes that I'm sure you have seen on the shelf at AutoZone and WalMart. Those work great. Decomissioned toothbrushes work great too. Last year I found an even better alternative to some of those tools though. They are called Slick Stixxx and they are one of the best detailing aides I've ever used. The handles are wrapped in silicone so that you don't have to worry about them scratching anything. There are multiple points and angled attachments to make getting even the hardest to reach area clean. Just wrap a worn microfiber towel around the point and jam that puppy wherever you need to get to. Then use a longer attachment to push it around the dirty areas and you'll be surprised how clean your engine will get. Don't be afraid to get your hands dirty on this. You only have to do it once and it will be easy to maintain from there on out.
Dry the engine well. This last step doesn't like to play well with standing water. Dry off everything you can and polish up the aluminum or chrome that you have showing. I use Eagle One Never Dull wadding on my chrome and aluminum to get the best shine possible. Some engines take more love than others, but nothing looks better than perfect chrome in the engine bay. The best part is that it is an easy product to find locally and it is even easier to use. Just pull off a piece and rub down the parts until they are shiny. Then wipe them down with a dry cloth and admire your work. Nothing easier than that.
Now would be a good time to make sure you didn't miss anything. Are all of the hoses clean? Did you get that junk out from around the oil cap? How about the reseviors? Are they all clean as well as the caps? Just take a minute and do a final inspection. This last step isn't something that is irreversible, but it is something that you really want to actually be the last thing you do before you close the lid. It sucks to pull the car out to show off your engine and then see a couple spots you missed behind all of the fabulous shine that you've got going on.
CD2 is a company that was bought by Turtle Wax a couple years ago. Until that point you could find one of their products called Engine Detailer on the shelves at several auto part stores. Then all of the sudden it just vanished. Nobody could find it anywhere. AutoZone used to be the only place I could find it and then suddenly even they didn't have it. I was forced to buy it off eBay or Amazon in order to get my hands on the good stuff. I was paying upwards of $12 per can for this stuff at one point, and then it suddenly came back. HAPPY DAY!!! The first thing I did was go out and buy fifteen cans of the stuff. I stocked my shelves well just in case it vanished again. The stuff is more addictive than crack and heroin combined. Just wait till you try it and then you'll understand.
CD2 Engine Detailer is to be sprayed on a cool dry engine. Techincally it is just for the rubber and plastic, but you can get it on chrome and paint as well. It won't really do much for those pieces, but you don't have to worry about harming them either. Of course, you still want to avoid the same spots that you watched out for during the degreasing and rinsing phases, but you should be a pro at that by now. ;) Spray the plastic and rubber with the Engine Detailer and make sure you get all the angles. You have to walk around the front of the car a couple times usually to get everything. I can usually get two or three cars out of a can of this stuff if I'm using it heavily. You should be able to get more distance if you have less plastic. TheLegacy GT has a lot of it, but my Corolla XRS doesn't have much at all. My Accord had even less, so you may be able to get a can to last you for many months. At about five bucks a can at AutoZone it isn't so pricey that you need to worry about it though.
The directions on the can say to close the hood and let the engine run for 20 minutes before you do the final wipe down. I've tried that lately and it does seem to produce good results. The heat sort of sets the product and all that is left is just excess. Wipe that off and you are good to go. When you first apply it you will notice that it is very wet looking. It dries to more of a matte shine after you heat it up and wipe it down. Don't worry about the shine for sure. Not only does it dull down a bit, it also doesn't become a dust magnet like other methods of shining the engine can cause. CD2 Engine Detailer is one of my favorite products around.
The bottom line is that engine detailing doesn't have to be ridiculously hard. You can do it yourself and get awesome results if you take your time. There is more risk in washing the engine bay than there is washing your car in general, but it is a risk that can be managed. Just take your time and be careful. As always, feel free to let me know if you have any questions. :)