How to Clean an Engine

Auto detailing's final touch: a shiny, clean engine

Article updated October 2011

Cleaning your engine may not be on the top of your car care list, but it should be close to the top. If you do your own engine service, a clean engine is a whole lot easier to work on. Note that you can clean your engine without compromising electrical parts, the environment, or yourself, thanks to a few simple precautions and the right tools.

As already mentioned, there are a number of practical reasons to include engine cleaning in your regular maintenance. Have you ever crawled around under a car as drops of oil and bits of grease fall into your eyes and hair? Or tried to find a tiny oil leak when the engine is coated with dirt and grime? Does it bother you when smears of road grime appear on your arms and hands after performing a simple tune up?

Spray Time

Dealing with grimy mechanicals is no way to work on a car. Oil leaks can be impossible to find when the whole engine is coated in black gunk. Even simple maintenance can start to look like a Superfund cleanup site. Not only that, slippery parts and tools can become dangerous when they start sliding out of your hands.

So if there are advantages to cleaning up an engine, why isn't it done more often? There are a number of reasons. One of the most important in the last few years is the damaging effect that water can have when forcibly sprayed into delicate electronic components and connectors. A clean engine isn't any good if it doesn't run.

Another problem is that cleanups can be plain messy and even environmentally hazardous. All of that dirt and oil has to go somewhere, and washing it down the gutter or splashing it into your face can be a bad idea. So how can we get the engine clean without damaging it, ourselves, or the planet?

Let's start with what you will need to do the job. First off, we should point out that there is no magic cleaner that will simply dissolve all of the hardened oil and grease off your engine. (If it's strong enough to do that, then it will probably dissolve some important engine parts as well.) All of the common cleaners and degreasers require you to do some scrubbing. Maybe even a lot of scrubbing. Some of the best cleaners available are the "environmentally friendly" type. They work very well and they don't kill you when you breathe some of the fumes.

The Brush Off

For the elbow grease part of engine cleanups, an old flathead screwdriver works well as a small scraper that can reach into tight corners and recesses. Also, a small toothbrush-sized wire brush will fit nicely into tight quarters and scrub away the toughest stuff.

If you do not have compressed air, consider buying a special misting nozzle for the end of your garden hose. These blow a fine spray of water out in very low volume, and not at a high pressure. It is important to avoid high pressures and large volumes of water. Steam cleaners and pressure washers are the opposite of what we want, because they can blow out gaskets, push water past seals into the engine, and force water right through all-weather electrical connectors. Be careful to use these type of washing methods only on non-vulnerable components because they can damage your engine.

How is the actual cleaning accomplished? The first thing to do is prepare the engine compartment for the treatment. This involves covering everything that should not come into contact with water, such as air filters and air inlet holes, breather caps on valve covers and oil filler caps. The dipstick tubes for engine oil and transmission fluid also need covering. Parts of the ignition should be covered, including the distributor and coil or coils. Other electronic parts that should be covered and avoided are fuse and relay boxes, wire connectors, and sensors.

Tool Time

Use plastic grocery bags with tape or rubber bands to secure them tightly. Do your very best in covering and sealing off these items from any and all water contamination. If they get even a small amount of moisture inside them, your car might run poorly, or perhaps not at all. If any of these items are dirty and you feel they need to be cleaned, then use a rag and carefully wipe them clean, rather than spraying and scrubbing.

Now you are ready to start scraping away the large chunks of grime, so that the degreaser can soak down to the engine when it is sprayed. Place a large drip pan underneath the area to be cleaned. All of the dirt and degreaser will fall into this, instead of on your driveway. After everything has been scraped, then it is time to apply the degreaser.

You can apply it in any way you see fit, but a spray bottle seems to be the easiest. Don't be stingy, Use enough to really wet down the dirty areas. You can let it soak for a few minutes, but it is a good idea to start scrubbing while things are still wet. It will be a slow and dirty process, but the end results will be surprising. This really is the only way to get the dirt out of every crevice.

After you feel that you have scrubbed all of the dirt loose, it is time to rinse. If you are using the compressed air sprayer, take care. The dirt and degreaser and water can get blown back onto you, so wear plenty of protective gear. A garden hose misting attachment will also work quite well in this situation, although it may be a little slower.

After you have rinsed off all of the loose degreaser and dirt, you will more than likely find all of the spots that you missed the first time around. Let the water dry off, then spray on more degreaser and start the scrubbing process again. Patience and time, that's all it takes. Eventually, you will have a very clean engine, one that can be kept looking good with just light touchups every so often.

The drip pan underneath the engine will have collected all of this water and dirt. Let the pan sit out for a couple of days so that the water can evaporate. What you will have left over is mostly grease, oil and dirt. These items can legally be put into your waste oil container that you use when making an oil change.

Once everything seems to have dried off, and you have removed all of the bags covering everything water sensitive, it is time to start the engine. If you have done everything right, it should have no problems starting right up and running fine. If not, then it is time to start searching for water where it doesn't belong. Most often it will be in the ignition system somewhere. Take care in your original covering of everything to avoid this problem.

Once you've done a good engine cleaning, your engine will not only look better, but also be much easier to service and repair. And if you're trying to sell you car, buyers will be more impressed by a clean, spotless engine. 

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