The fit and finish of a car's exterior often gets all the attention, and most gearheads will debate polishes and paint protectants for hours on end. If you want to find who is really detail-oriented at a car show, don't look at the hood—look under the hood. A spotless engine bay is tough to achieve and even harder to maintain. It's worth it, though, because a clean engine compartment is not only attractive but also conducive to spotting any leaks or issues when they start, rather than leaving them to be camouflaged by grime.
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Soften heavy, greasy gunk with your favorite penetrating oil (WD, JB, Kroil, Rost Off, whatevs) before you reach for the cleaner. Cleaners typically pull out the oils, which just makes the gunk more solid. Saturate it with spray oil (let it soak if needed) and wipe with paper towels. Repeat until it's clean. Yes, it will probably take a couple of tries, but it will leave a shiny finish which will protect against corrosion. You might even decide to skip the cleaner and leave it as-is.
I've been using a pressure cleaner with plain water for decades to clean engine compartments. It works very well, has no harmful chemicals and is efficient. The trick to using a pressure washer in the engine compartment is to know what components to stay away from and how close to a particular component one can get. The farther away, the less pressure. I don't recommend using this tool if you haven't done it before. Get a little carried away and you'll be replacing parts.
Remember, Oil and grease are soluble in...well oil. A little fresh cheap oil will loosen grease and grime when using a scrub brush. Afterward you can rinse with water and a mild detergent such as Dawn. I also like WD-40. It helps clean and is safe on your hands.
For areas that are extremely "gunked up", I have had good luck covering the end of a flat screwdrive with a shop rag and loosening/removing the heavy stuff prior to applying a degreaser.
Got a point-style distributor? Grab a plastic shower cap and a zip tie. Pull the cap down over the cap and wires as far down as you can get it and snug it up with the zip tie before you get anything wet. And if you have any anodized parts like A/N hose ends or rocker covers, stay away from carburetor cleaner. It tends to strip the dye off of aluminum, leaving it streaky. I've had luck using 409 and an old toothbrush getting grime off of intake manifolds and cylinder heads. By the way, WD 40 is also an excellent solvent for cleaning slightly oily surfaces. Scrub the parts gently and wipe them dry. Allow the vapor to dissipate (about fifteen minutes) and go cruise.
I always used the H.D. engine cleaner, "Gunk", which I dilute with kerosene. I spray or brush this on everything and let it rest for an hour or more. After that, I rinse with the
garden hose without a high pressure nozzle. Works like a charm. Gunk is in all auto stores. Or go to your nearest Harley dealer.
On vehicles from the 90s there is quite a bit of brittle plastic under the hood. I would never use a power washer on a vehicle of this vintage. I found that simple surface wipes work well. Wondering what your thoughts are on plastic renewal products ... ArmorAll? Forever Black? Etc. Cheers!
Having cleaned literally hundreds of engine bays over the years as a lifelong hobbyist and classic car business owner, it is amazing how few products and tools will get the job done. A toothbrush, 3 or 4 cleaning cloths, 409 or your favorite degreaser, effort, and an eye for detail will go 85% of the way. The rest will involve removing parts to refinish, or touching them up in place with the appropriate finish, paint, polish, or abrasive tool. And I can't emphasize how much taking your time will help. Doing one section of the engine compartment at a time (however you choose to break it down) can also extend your patience and, ultimately, your satisfaction.
I've had literally hundreds of worn-out t-shirts over the years, and (cut up) they work fine as engine-bay rags. I haven't bought a rag - other than for exterior cleaning - in years. Firewalls and inner fenders are typically not as crucial as exterior finishes when it comes to cleaning, so t-shirt material suffices.
About every two years we just pull the mill out clean it completely, mask everything and paint it. After you've done it once or twice its a piece of cake. You know what wrenches to pull out of the box, where all the nuts and bolts are, what order to remove them, the best way to rig the hoist etc,etc. Does not take that long. Additionally if any maintenance is required its a lot easier on the engine stand than in the engine bay.
Its really not as difficult as it sounds and the engine bay looks great. Folks always comment on how nice and new it looks.
Ever since I completed my restoration of my e-type which included the engine compartment I have washed the engine down with GUNK. I normally wash the entire engine and surrounding areas at least once every other month while washing the car and the engine compartment stays spotless.
We owned a Mercedes AMG C63 awhile back and it developed an engine miss. The local Mercedes dealer checked it and recommended a new $14,000 engine bay wiring harness. The next farther Mercedes dealer said it needed $28,000 worth of repair. A friend told us about this old guy who's pretty sharp with cars. He diagnosed & had it running perfectly in twenty minutes; for $80. The problem? a friend who I let use the car had it detailed and water went into the spark plug wells, shorting out several coil packs. The old guy had a couple of used ones on hand and in no time everything was good again.
Two tips: (1) It's easier to maintain a clean engine bay than to wait until it's Grunge City. Of course, if you are resurrecting a barn find, or worse, a back-of-the-garage find, you need to do the heavy duty stuff. But keeping a new car clean, even after 15 years, is way easier and needs less invasive chemicals and procedures. Generally, I clean the engine bays every other car wash. Good old Lemon Pledge works fine. (2) Motorcyclists have been using S100 for decades. It not only works on all levels of dirt, but it leaves a nice finish on metal, rubber and plastic surfaces. You DO have to rinse with a hose, so take the necessary precautions. However, I have found that if your car can keep running fine after driving through a puddle, you don't have to go crazy. FOLLOW THE DIRECTIONS!!! S100 can be found at any bike shop, but be careful as they make you walk past all the motorcycles to get to the parts department.
After having spent the winter excavating my 62 Sunbeam engine bay and underside from layers of grime, I would second what dough says - there's no miracle product or replacement for good ol' elbow grease. I would add a shout out tho to citrus cleaner - Blaster makes a good one. Smells nice, a little less toxic and pretty effective at eating thru grease.
I live in Maine, so I like to splatter extra oil on things. Great way to dispose of my 6 gallon oil change leftovers, great rust prevention. My frame gets a regular oil glaze as well. Filth and oily sludge isn't always a bad thing
Yeah, that's why I loosen a few pan bolts on both the engine and tranny - let a little of that stuff leak out and cover the entire undercarriage. Never understood why they make those darned gaskets so efficient at sealing. Cheap undercoating, eh? 😆
Simple Green and water 50/50 (with some scrubbing with a brush or rag) will usually take off any reasonable amount of grime. I use it 100% under the car as well. This is always followed up with spraying water from a garden hose over the compartment. Then blow off the remaining moisture with a leaf blower followed by drying rags.
The trick I use (taught to me about 30 years ago) is: once you have your engine compartment cleaned then every couple of weeks or more if you drive less, soak down the entire engine bay with straight Simple Green (BTW the engine needs to be stone cold), let stand for a few minutes (Brush stubborn stuff with a soft bristle brush) then rinse throughly with garden hose.... I have kept all my car's engine bays cleaned this way for many years...
I also think dough has the most accurate assessment in my experience. That’s exactly what I did with mine and the before and after pictures are remarkable. Replaced as many rubber hoses as I could match, cleaned one part at a time, and removed and painted parts. Took apart things that I had no intention of removing but turned out necessary, and carried out some maintenance while I was at it. I open my hood proudly now.
Oh I agree. I've had guys argue throughout an entire 6-hour-long car show just about that subject. Although what "rag" or "cloth" to use to apply or wipe off the detailing product can be almost as touchy a subject. It's amazing to listen to the loyalty - and the bashing... 😄
A starting point on a recent cleanup of an old car engine area dirty, greasy, and gritty responded well to rags soaked in diesel fuel. I may actually be able to go directly to painting because the diesel dries clean.
The motor on my 1971 240 Z doesn't get greasy, but dusty at car shows. So a garden hose washes off the dust, then my leaf blower quickly removes All the water. My polished valve cover, chrome etc comes out perfect and quick. Then wash the body.
Using just the right amount of detergent and water especially under pressure can be delicate work. I use a small pressure sprayer communally used for lawn and pest sprays It can be found inexpensively at your local home improvement center. The wand reaches tight spaces and you have a precise control of the flow. Use your favorite degreaser, agitate thick stuff with a nylon dish brush from the dollar store and rinse off with the sprayer. A small wet/dry shop vac will also help. First by vacuuming up all the loose detritus in the engine bay. Then after wet cleaning you can both suck up excess liquid that has settled and is not draining or reverse the hose to the outlet side and blow stuff out of tight places if you do not have compressed air available.
I am a big fan of WD40. Spray a can on the entire engine compartment (no belts) and let it sit. Then get some red garage rags and start wiping it clean, using a tooth brush or whatever is necessary for smaller, hard to reach areas. Then I spray it again and keep it up until it's clean. Sometimes I do it over time, letting it get cleaner each time. I always spray the engine down lightly when finished to prevent rust and corrosion. While the WD40 gathers a little dust, it retards the rust, so I just wipe it down occassionally and spray it again. It makes ones engine look new over time, except for engines neglected for long periods. BTW, I use this on my regular use vehicles too. My engine bay always looks new.