How to Clean an Engine Bay – Step by Step and What NOT to do!

There are many aspects of vehicle maintenance. There are obligatory things that have to be done regularly, like oil changes and checking your tire pressure.

Some tasks aren’t necessary but highly recommended to keep your car in good shape. One example is applying a good paint sealant every so often to preserve the exterior.

Other jobs fall under the category of being, for the most part, voluntary choices. They can be beneficial to perform under certain circumstances. Cleaning an engine bay is one such task.

Close up of an immaculately clean car engine bay

In this article, you’ll learn when and why you might want to make an effort to clean this area out. We’ve answered whether spraying water into the bay is safe and what precautions to take when doing so.

We’ve provided instructions for how to protect vulnerable areas as you work. There are also tips for picking an appropriate work area since it can get messy. Every step from preparation, to drying it off to finish is explained.

Skill Level: Beginner.

Time to Complete: 30 minutes to 1 hour, depending on the size and condition of the bay.

Tools Needed:

  • Gloves, safety goggles and mask.
  • Engine degreaser, (Choose one from our guide to the best engine degreasers.)
  • Engine bay sealant or polishing products (optional).
  • Shop vacuum.
  • Plastic bags (e.g. shopping bags, trash bags, etc).
  • Cling film.
  • Masking tape.
  • Car shampoo.
  • A bucket.
  • Spray bottle.
  • A pressure washer for cars or garden hose.
  • Sweep brush.
  • Wash brush with soft bristles.
  • Car wash mitt or sponge. (Check out our guide for the best car wash mitts)
  • Shop towels or clean rags.
  • Large drip pan and absorbent pads, if you’re working from home.
  • A leaf blower or hair dryer.

Why Clean Your Engine Bay? What are the Benefits?

For one, performing an engine bay cleaning is something any vehicle owner can do. Automotive expertise isn’t a prerequisite.

All you need is common sense and a little bit of patience. If you’re still hesitant about moving forward, let’s talk about the benefits.

Improve Performance

Getting rid of layers of gunk and filth can help to keep your motor running cooler.

Enough dirt buildup can increase operating temperatures, which lessens the overall performance of your engine.

After Repairing a Leak

As much as we don’t want them to, leaks happen. Coolant, oil, and even fuel can spread to unlikely places.

Once the breach is repaired, you may want to clean the residue out of your motor. Splashes of these fluids can heat up and vaporize when you’re running your vehicle.

The smell of burning oil, gasoline, or coolant isn’t pleasant. These fumes can also be toxic. For example, antifreeze vapor can irritate your respiratory tract, skin, and eyes. Inhaling gasoline can cause headaches and dizziness. These aren’t ideal conditions to be operating a car.

On a less serious note, these sticky substances can attract grime. Dust and other debris can build up at the site of the puddles.

Preparing to Sell

When you sell your car, you want to present it in the best possible light. It’s only natural that a potential buyer will want to look under the hood.

If it’s filthy and greasy, it will be hard to inspect. That also won’t give a good impression; the buyer might suspect a leak or even feel that the vehicle hasn’t been looked after properly.

Performing a Deep Clean

You may be planning to give your car a hood-to-grille cleaning. Why neglect the engine compartment?

You can enjoy the satisfaction of knowing the entire vehicle is spotless inside and out. If you’ve already set time aside for this, an extra hour for the bay won’t hurt.

Can You Spray Water Into an Engine Bay?

The answer is yes, but with a few constraints. As long as you keep these in mind, you shouldn’t have any trouble.

Avoid High Pressure

If your vehicle were human, the bay would be where all vital organs are located. A gentle approach is critical for a successful, damage-free cleaning.

Those of you with pressure washers, forget about higher settings. High-pressure streams may do a better job at removing filth, but can also be destructive. Powerful pressures can dislodge parts from the bay, posing a safety risk and causing damage.

If you have a garden hose, you don’t need to twist the knob to the maximum. A steady low-pressure stream will suffice.

Don’t Flood Anything

Make sure to keep your hose or pressure washer moving while you’re spraying water. Don’t drift off into your thoughts and aim the nozzle at one spot for too long. Water could be forced into places that shouldn’t be flooded.

Be Careful to Shield Vulnerable Parts

Some components should stay dry during the process. You have to take the time to cover them before you begin. With these parts shielded, you can spray water without worry.

This includes any exposed electrical connections and any holes or crevices where water may be able to get in.

Spread Out Your Cleanings

This isn’t a chore you should do frequently, even if you enjoy it. Regularly spraying your motor with water—say, every week—can lead to corrosion.

Once or twice a year is fine for the majority of vehicles. You can also wash it after the discovery and repair of a moderate to severe leak.

Choosing Where You’ll Be Working

You’ll probably be shocked at what will come out of the bay. Road grime, dust or oil residue, the runoff will be nasty and can make a real mess of the driveway, roadside or wherever it is that you’re working.

So choose your workspace with care. You can’t park your vehicle in any old place and start cleaning it.

If Working at Home, a Drip Pan is Obligatory

You likely saw that we mentioned a drip pan and absorbent pads are optional. If you’re renting a space to work in for the day, you probably won’t need one. The floor will have built-in drains for toxic waste. You won’t have this advantage if you’re parked on your driveway or street.

Runoff that’s contaminated with oil, fuel or coolant is an environmental hazard. You can’t allow it to puddle on the street or get into storm drains. This is considered polluting as it can degrade local water quality. In lakes or streams, this toxic waste can affect local wildlife.

Pets and young family members also walk through puddles outside. This is a risk you don’t want to take so use a drip pan.

Good Lighting

On a gloomy day or at twilight isn’t the right time to get started. You need to be able to see what you’re doing as you wash. If not, you could accidentally wet coverings or leave some areas dirty.

How to Clean an Engine Bay – Start to Finish, With Safety in Mind

Allow Engine to Cool Before Starting

Your motor has to be completely cool. This is partially for your own safety to prevent burns. But additionally, heated components won’t appreciate being sprayed with cold water and could be damaged.

Check Caps, Lids and Dipsticks are Tight

Once the motor is cool, the next step is checking that caps, lids, and dipsticks are secure. Ensure reservoir lids for the coolant and brake fluid are fitted tightly.

Give caps a twist to be sure nothing is loose. It’s imperative that water and cleaning products don’t enter into any of these places. You don’t want these fluids circulating inside your vehicle.

Remove Battery (if You Can)

Beginners are welcome to skip ahead to the next step. There’s nothing wrong with keeping your battery in so long as you cover it properly.

If you want a 100 percent guarantee it won’t get wet, take it out. This is how to do it:

Step1: Prepare Tools and Use Gloves

Get your socket wrench out and put your gloves on. Attach the socket that fits the nuts on your battery to it.

Step 2: Disconnect Negative Terminal

The negative terminal can be identified by the minus sign near the cap. Use your socket wrench to loosen it.

It’s essential to disconnect the negative terminal before the positive one. This way, it eliminates the chances of arcs occurring.

Once it’s loose, move the negative connector to the side. Position it in a way that it can’t make contact with the terminal anymore.

Step 3: Repeat for Positive Terminal

Repeat the same process for the positive terminal. Take care to position the connector away from the terminal and metal surfaces. The connector will carry a residual charge.

Step 4: Unscrew Brackets

Your battery is held to a tray by brackets. You’ll have to unscrew these to be able to take it out.

Step 5: Lift Battery Out (Don’t Hurt Yourself)

You may want to have someone assist you, as the unit can weigh 30 pounds or more. Lift it out of the tray, keeping it straight.

Avoid letting the battery hit or scrape against other parts of the vehicle. Store the battery in a safe location away from direct sunlight.

What Components Should Be Covered and How?

You can’t dismantle every component that shouldn’t get wet. They’ll have to be covered with plastic bags or cling film.

If you’re using old bags, check them for holes. A tattered or torn bag will defeat the purpose.

List Everything You Covered

Driving around with plastic still floating around your motor can be disastrous. If you’re forgetful, make a list of every component you covered. This way, once you’re done you’ll know how many coverings to take out.

Caps and Dipsticks

Place a bag over each cap and dipstick. Use your tape to secure each one to prevent it from moving around.

Battery (if Not Removed)

Disconnect the battery if you haven’t done so already. Cover it with a large plastic bag as well as you can.

Electronic Mechanisms

Electricity and water don’t mix. Luckily, modern vehicles are better insulated in this respect, there’s less to protect than with older vehicles.

Use your cling film, tape and plastic bags to cover the following:

  • Spark plugs.
  • Alternator.
  • Ignition coils.
  • Fuse box.
  • Any other exposed electronic mechanism (e.g. connectors and plugs).

Air Filter

Cover the air filter, another part that shouldn’t get wet.

Special Precautions for Antique or Heavily Modified Vehicles

Older cars and modified vehicles may have additional components that need covering. Examples include carburetors, which almost all modern engines are built without, distributors, electrical connections, etc.

The same applies for turbocharged or supercharged motors. Cover all modified, water-sensitive parts as needed.

Prepare Safety Equipment and Supplies

Set up your work area and have all your supplies at the ready. After this, the real work will begin.

Step 1: Goggles and Gloves On

Get your gloves and goggles out and put them on. You’ll be keeping both on until the last rinse-off.

Step 2: Keep all Supplies Close

Your degreaser, scrub brush, car soap—everything needs to be close by.

Step 3: Drainage Pan and Absorbent Pads

Place your drainage pan squarely underneath the engine bay. Place your pads evenly throughout it.

Brush and Vacuum Loose Dust and Dirt

Make things easier for your degreasing product. Clear out as much dirt as you can before applying it.

Step 1: Take Out Solid Debris

Pick out larger bits of debris, like twigs or leaves.

Step 2: Sweep Wherever You Can Reach

Sweep over the motor and sides of the engine bay. Your mask will keep you from inhaling any clouds of dust.

Step 3: Start Vacuuming

Using a slim nozzle attachment, vacuum exposed surfaces. Don’t force or jam the vacuum head into places it won’t fit.

Wet Engine Bay Before Applying Cleaning Products

A preliminary rinse will take off the layers of loose dirt, dust and grime you didn’t catch.

Step 1: if Using a Pressure Washer, Check Setting Is Low

Double-check that the pressure is at the lowest setting. If not, you’ll be surprised by a powerful jet of water instead of a mild one.

Step 2: Rinse the Bay

Rinse the entire engine bay, avoiding the parts you covered. Try to avoid wetting wires more than you absolutely have to. Remember not to spray water in any one area for too long.

Apply Cleaning Product or Degreaser

Take out your cleaning product or degreaser. This substance is going to do the bulk of the hard work for you.

Step 1: Transfer Product to Spray Bottle (If Needed)

If the product doesn’t already come as a spray, you might want to change this. Putting it into a spray bottle will make application easier.

Step 2: Follow Preparation Instructions

Read the instructions for the product you chose. You may have to dilute it with water first or shake the canister for a little while.

Step 3: Apply to Entire Engine Bay

Coat all exposed surfaces liberally with the degreaser. Start from the bottom up so you don’t accidentally rub the product off as you’re applying it.

Don’t forget to cover:

  • The engine itself.
  • Master cylinder.
  • Radiator.
  • Air conditioner.
  • Oil pan.
  • Power steering pump.
  • Water pump.
  • Windshield wiper fluid reservoir.
  • Coolant reservoir.
  • The firewall, sides, and front of the bay.

Step 4: Scrub Stubborn Spots

Use your soft-bristled scrub brush to distribute the degreaser and scrub stubborn grease. Do so gently, as you don’t want to scratch anything.

Step 5: Let it Sit

Give the degreasing product time to work its magic. Usually, you’ll have to give it between 5 and 10 minutes.

Step 6: Rinse Off Degreaser

Once enough time has passed, rinse the product off. Pass the hose or pressure washer evenly over the area until all traces of product and dirt is removed.

Check your drain pan every so often to check that the absorbent pads aren’t saturated. If they are, you’ll have to replace them with dry ones. Dispose of the soiled pads in a garbage bag.

Step 7: Repeat Application

One application may not cut through years or thousands of miles worth of grime. If the bay is still looking rough, apply your degreaser again.

Rinse it off in the same manner as you did the first time. Don’t forget to make sure your drain pan isn’t overflowing.

Use Your Car Shampoo

Car shampoo is the final touch to clear off the remaining residue. If you happen to have a foam cannon at home, this is a good time to use it.

Step 1: Mix Car Shampoo and Water

Dilute your car shampoo in water, mixing the two in your bucket. If you have a car cleaning foam cannon, fill up the canister.

Step 2: Apply Soap to Uncovered Areas

Soap up all the exposed surfaces using your car wash mitt or sponge. Try to wring the mitt or sponge out so that it isn’t soaking wet.

Use your discretion when you decide how hard to scrub. Rubber hoses should be done with a lighter touch than the walls of the bay.

Step 3: Last Rinse

This is your final rinse, so be as thorough as you can.

Final Dry Off

Now that everything is pristine, you need to dry the compartment out. Prepare your shop towels (or clean rags).

Step 1: Shop Towels or Rags

Wipe down everything you can reach without getting your hand stuck. Use as many towels or rags as you need until the bay is as dry as you can get it.

Step 2: Leaf Blower or Hair Dryer

A hair dryer or a leaf blower set to low will dispel residual water. Pass your tool of choice all over the compartment. You may have to repeat this several times.

Apply Sealant or Polishing Products

As an extra touch, you can apply a sealant to the bay to protect it and keep it cleaner for longer.

There are also polishing products for metals and plastics that will get internal mechanisms gleaming. If you choose to use these – and it’s completely non-essential – then make sure to follow any product instructions!

Replace or Reconnect Battery and Remove Anything Used to Cover Components

Now that the bay looks good, it’s time to return it to a functioning state.

Step 1: Remove all Covers First

Take off all covers: your bags, cling film and tape. If you made a list of what you covered earlier, consult it now to make sure you get every last one.

Step 2: Reconnect or Replace Battery

If you removed it, bring the battery back and set it into the tray. If you had a person help you lift it out, call them back for help.

Screw the brackets back on and reconnect the terminals. Batteries that weren’t removed will only have to be reconnected.

Always begin with the negative terminal, even when reconnecting. There’s no need to end the day by getting shocked.

Start Engine to Dry it Thoroughly

You can now safely switch on your engine. Let your vehicle idle for ten to fifteen minutes so that any damp patches evaporate.

Once dry, your engine bay cleaning is complete.

Final Thoughts

You might not be able to appreciate the results the same way as with an exterior wash. Still, you can have the satisfaction of knowing your car’s inner works are immaculate.

Learning how to clean an engine bay is a practical skill to have. You can prepare your vehicle if you need to sell it, or wash the bay of a secondhand purchase.

Washing it every so often will also improve lifespan and performance. Nasty debris won’t have a chance to cause corrosion or build-up and provoke overheating.

Do you have questions for us? Have you made any mistakes or successfully cleaned an engine bay before? Please let us know in the comments section below.

Kyle Palmer

From childhood go karting and motocross, to collecting and obsessing over scalextric, matchbox and radio controlled cars, I've always had an obsession with cars. Learning through manuals, books, trial and error, and more knowledgeable family members, I've also enjoyed tinkering with the mechanics and electronics of any vehicles I've owned. Now, over 3 decades later, I've started this site as a place for me to share my knowledge, to teach others how to care for and maintain their vehicles themselves, at home, so they can get the most of their vehicles and save a pretty penny compared to always seeking out professional help.

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