3 dos and don’ts for cleaning your engine compartment

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Kyle Smith

The fit and finish of a car’s exterior often gets all the attention, and most gearheads will debate cleaning materials like 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.

If your engine is a dingy, oily mess and you want to bring it back to a respectable condition, here are a few tips.

Don’t: Be quick to take things apart

Do: Take a “before” picture

Corvair engine compartment torn down
The last thing anyone wants is to get here and forget how it goes back together. Kyle Smith

If the engine is running smoothly, I’m hesitant to take anything apart to clean it, and I’d recommend you think the same way. The old adage of “if it ain’t broke, don’t fix it” has treated me well for many years. However, to get a deep clean you must dive deep. Before you start, grab your camera and snap a picture.

Even if you have a great memory and a wealth of reference materials, a photo can still prove invaluable. Sometimes, all it takes is a simple glance at a “before” picture to know where that hose with the weird bend was attached. It also serves as great evidence of the improvement you make.

Don’t: Go crazy with the “engine cleaner”

Do: Use chemicals appropriate for the job

Three cleaners for engine detailing
Here are three chemicals of varying intensity. I start with the mildest and progress to the most aggressive, making sure that even the strongest will not damage the finish on the parts I am cleaning. Kyle Smith

It’s on a shelf at every auto parts store—you’ll be tempted to grab that aerosol can of foaming degreaser and pretend you are the greatest graffiti artist known to man as you fog the entire engine compartment. Don’t do it.

Aerosol engine cleaner works great for engines that are very heavily soiled, but most of the time that stuff is overkill. It’s also deceptively involved; if you don’t rinse off all the residue, it will cause corrosion. Instead, spend a little extra time by using a few clean rags, spraying your detailer of choice on the rag, and simply wiping away the dirt. I typically start with a quick detailer and, if the grime is stubborn, I progress to more aggressive chemicals like brake or carburetor cleaner.

This more time-consuming process has two benefits: It prevents chemicals from forcing their way into nooks and crannies they shouldn’t be in, and helps you become familiar with those same nooks and crannies. Seeing a lot of oily buildup in one spot? Investigate to see whether there’s a leak that needs to be cured.

Don’t: Grab the pressure washer

Do: Use the garden hose

Model A engine compartment
Hosing down my Corvair’s engine doesn’t make sense because it won’t drain water like most engine compartments. Rinsing this Model A, on the other hand, might be the easiest way to remove lots of sludge. Kyle Smith

If you need to wash off the grit and grime, resist the urge to reach for the pressure washer. Both a home pressure washer and the wand at a local DIY car wash will eject water at a dangerously high pressure and threaten just about any part of your engine compartment. The jet can easily push past gaskets, into electrical panels and connections, and also into grease fittings.

If you discover the engine compartment is so filthy that a rinse-down is needed, take the time to seal all electrical connections and crankcase openings (the oil fill, for example) before using a garden hose. If the garden hose doesn’t provide enough pressure, gently scrub with a soft bristle brush to break the gunk free.

What is your process for cleaning your engine compartment? Sound off in the Hagerty Community below.

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