How To Wash Your Engine Bay: The Safe Way to Make Your Engine LAST

Categories: Engine
A BMW engine bay in need of a thorough washing
A BMW engine bay in need of a thorough washing

So, you just opened your hood for the first time since the winter and almost fainted. I don’t blame you. I usually do too, so I decided to whip up this post on how to wash your engine bay!

I personally dread opening a dirty engine bay any time after fall. It’s always a disaster. All that snow slurry and road salt your wipers spent months clearing off your windshield have also been building up in your car engine bay, passing through your radiator and getting kicked up from underneath by the road itself.

But, as a car owner, you can’t afford to ignore it. Modern engine bays are simply packed with sensitive electronics, sensors, an engine control unit, miles of wire, and hundreds of electrical connections. Salt is trying to get into all of them, corroding leads, causing shorts, and throwing error codes. It’s gotta go.

Even if you’re not stuck in snowy hell 4-6 months a year, it’s important to learn how to wash your engine bay so you can keep your engine clean and running well just like the rest of your car. Dirt and grime build up and act as a blanket, trapping heat inside your engine that would otherwise radiate away, putting more stress on your cooling system and hurting both performance and fuel efficiency.

A clean engine bay is a cool engine bay, and a cool engine bay is a happy engine bay.

…but don’t just grab a hose and go to town.

The same sensitive electrical components you’re trying to defend from salt are also not enormous fans of water for obvious reasons. You’re going to want to learn how to clean your engine bay safely, otherwise, you risk doing more harm than good.

How To Clean Your Engine Bay: If You Hire Out the Job

The safest way to wash a car’s engine bay is dry ice blasting. Think sand blasting except the medium is frozen carbon dioxide instead of sand. It’s much less abrasive than sand and won’t hurt even the plastic or rubber components in your engine bay. And because it’s just frozen carbon dioxide, there’s no water or moisture involved that could short out the electronics. Best of all, it will clean everything. Seriously, go watch a few dry ice blasting videos on YouTube. It’s mesmerizing. Like watching pressure-washers clean sidewalks and siding. And if you’ve never done that, holy crap. I borrowed one from a buddy and before I knew it, I’d spent an entire day pressure-washing everything on my property that wasn’t grass. Most major cities have restoration services which offer dry ice blasting, but the drawback is it doesn’t come cheap and you’re probably not going to be able to rent a unit to take home.

How To Clean Your Engine Bay Safely at Home: Your DIY Step-by-Step Guide

For the do-it-yourselfer in a garage or driveway, there are other options for cleaning your engine bay. Here’s how to clean your engine bay safely and effectively—at home!

Step 1: Let the Car Sit Overnight

You don’t want to wash a hot engine. Start early morning on a warm day you don’t need to use the car.

Step 2: Disconnect the Battery

This is critically important. Pull the negative battery terminal, hell, pull both battery terminals. If there’s no electricity flowing through the system, you can’t cause any short circuits.

Step 3: Protect the Electronics

You know that plastic grocery bag in your pantry or the one kitchen drawer stuffed with other plastic grocery bags? Congrats, you just found a use for it. Cover up major exposed electronic components like the battery, engine bay fuse boxes, CPU, basically anything with a ton of wires plugging into it. Also, most cars don’t have an exposed air filter, but some performance models do. If you own one of these sexy beasts, cover it up.

Step 4: Loosen Up the Dirt Before You Rinse

Pre-soak the entire engine compartment with a spray bottle of de-greasing agent like Simple Green or equivalent. Really lay it down, then walk away for fifteen or twenty minutes to let it penetrate deep into all the oil and grit. This will loosen up all the road grime and make it much easier to scrub off and hose away the loose dirt later. And don’t forget the radiator. The more road crap you can blast out of it, the more efficient your cooling system will be. While you’re checking, does your radiator have a lot of bent or crushed fins? This impact damage from road debris reduces the airflow rate through the radiator and lowers its ability to shed heat. Get a radiator comb and straighten them out. Bonus, it’ll work on your house’s AC radiator unit, too.

Step 5: Time for Brushes and Elbow Grease

Grab a stiff bristle detailing brush and get scrubbing. Get down in the crevices and creases, anywhere you see engine degreaser pooling. Avoid using steel or brass bristle brushes on plastic components; you don’t want to leave scratches. Plastic-bristle detail brushes are best here. The exception is on aluminum or steel engine components that have started to oxidize, like heads, air intakes, throttle bodies, etc. If you see red or brownish rust on the steel or a white, powdery substance on aluminum pieces, that’s oxidation. Scrub it off with a brass bristle brush, which is softer than either and won’t damage the healthy metal parts underneath. If you’re really anal, use a metal polish like Mother’s to shine up the freshly exposed surfaces.

Step 6: Wash, Rinse, Repeat

Don’t just use a garden hose. Use any spray nozzle that creates high pressure and decreases the water volume. Ideally, use a portable pressure washer, the sort you’d use to clean sidewalks or fences. Avoid spraying directly on sensitive areas like fuse boxes, sensors, spark plugs, coil packs, ignition wires, distributor caps, etc. Even those you’ve covered with the grocery bags. Hose it down until all the degreaser is gone and the wastewater runs clear.

Step 7: Finishing Touches

Once you’ve thoroughly washed and given a final rinse to everything, towel down any excess water, then wipe down all the rubber and plastic components with a conditioner like Armor All to keep them supple and prevent them from drying out and cracking. While you’re in there, check your serpentine belt for cracks or chunks missing from the rubber ribs on the inside surface that contacts the pulleys. If it’s looking worn or the belt is starting to fray, it’s time to replace it. Do Not put conditioner on the serpentine belt. It’ll cause the belt to slip and can actually decrease its lifespan.

Good work, you’re done. Walk away. Let the sun and breeze do the job of evaporating any remaining water you can’t see. Give it the rest of the day with the hood open before pulling the plastic bags, reconnecting the battery, and firing it up.

Congrats! Now You Know How To Wash Your Engine Bay

A Spotless Small Block Chevy V8 washed and ready for the concourse.
A Spotless Small Block Chevy V8 washed and ready for the concourse.

See? That wasn’t so bad, right? And now your engine bay looks ready for a car show. Make it a point to go through these steps every spring and the dirt, salt, and grease will never get an opportunity to really cake in and bake on. Your engine will thank you down the road, and so will your wallet.