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3 Problems You Might Have If You Wash Your Car Engine

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Car detailing manual car washing the engine with pressure water from a nozzle close up

Many vehicle owners wonder whether it’s a good idea to wash the engine of their car, truck, or SUV. After all, we wash our cars’ exteriors, so why not the engine? While it is possible to wash an engine, the project involves quite a few risks and hazards to be aware of.

Possible problems that you may incur as your attempt to wash your car engine could include damage to sensitive electrical components, water leaking into the engine, and damage to the engine itself if sprayed down too intensively. Having said that, there are safe ways to get your car engine clean, and we’ll go over these tactics, too.

Keep reading to learn more about the dangers and pitfalls involved in washing your car engine, as well as learn safer and more careful ways to make your engine bay look great and work beautifully.

Water Can Damage an Engine Bay

While water does a great job cleaning the outside of your vehicle, it can be harmful to the engine bay. This is thanks to the sheer number of interconnected and sometimes rather sensitive metal, plastic, and electrical parts of your vehicle.

Modern cars and trucks have increasingly complex electrical systems, and can easily be described as a computer of wheels. All of the sensitive electronic components of modern vehicles can be susceptible to moisture, and an excess of moisture can be catastrophic.

In addition, an excessive amount of water can leak into cracks and crevices and cause damage to an engine if the water exposure is prolonged or too intense. And if your alternator gets wet, it can mean the end of your car’s drivability for good. 

Finally, spraying down a hot engine with cool water can cause eventual damage to the engine, as metal doesn’t like to be cooled rapidly. If you do wash your engine, let the engine cool on its own, and don’t try to speed up the process.

Washing a car engine detailing auto service with pressure water

Water Can Damage Sensors and Wires

Some of the most important functions of a vehicle are now controlled by hundreds of tiny chips, and modern cars are increasingly digital and dependent on electricity rather than gasoline alone.

Features that used to be optional luxury specs 40 years ago (like cruise control and motorized windows and seats) are expected base-level features today, and the more advanced cars become, the more computer-like they are.

This means that your engine bay may house, or allow access to, a wide variety of electrical units and sensitive wired connections that you wouldn’t find in a ’70s muscle car. These items can become seriously damaged or fail if exposed to water.

Getting water on the alternator is especially dangerous, as this part helps convert battery power into the energy that makes everything from the ignition to the lights work on your vehicle. Once the alternator fails, your car will become the world’s coolest, most expensive paperweight.

While alternators can handle very mild amounts of water in the form of a rain shower or car wash, they’ll fail if submerged, or if exposed directly to moderate amounts of water. This is why it is so important to be careful when using water in your engine bay and be aware that just because your car or truck is built tough, it’s not indestructible.

Close up of the ABS module and wires covered in soap foam ready to be cleaned with pressure water

Water Can Leak into Your Engine

In extreme cases, water can even leak into the engine itself, and cause damage or engine failure. While modern engines are protected by hard plastic casing, these casings are not impervious, and if you use enough water moisture can seep in, and cause harm.

Water engineering your engine can lead to serious compression and pressure issues, which can damage or ruin the engine, and cause harm to people, too.

This is called “Hydrolocking” and happens when water gets into an area where vapor is supposed to be compressed. The piston and connecting rod cannot handle the compression of liquid and can warp, bend, or break under the strain of attempting this.

The engine may also face corrosion as a result of being in contact with water, and this corrosion will ruin the engine over time. Either way you look at it, getting any water into your engine is a recipe for disaster.

Spraying a Hot Engine to Cool It Can Cause Damage

While it might seem sensible to spray down a hot engine to cool it for easier washing, this is actually a bad idea. Your engine needs to cool down naturally on its own. Shocking the engine with a spray of cool water when it’s super hot can cause damage through warping and cracking.

While modern engines are generally well protected from water, the metal of your engine can face breakage and will still be sensitive to rapid changes in temperature.

It’s never a good idea to rapidly cool a hot car component, as this stresses the basic structure of the metal or plastic, which can break down the integrity of the item. This poses a huge safety concern with many parts, especially something as vital as the engine.

Older engines can crack, too. Yep, if your older vehicle engine is made of cast iron, the entire system can crack apart under the shock caused by pouring or spraying cold water onto a hot engine. The cylinder block will look like a piece of fragile pottery, and your engine will be ruined. Never do this.

An engine covered in soap ready to be pressure washed with water

Does A Car Engine Need to Be Washed?

Washing a car engine is primarily a matter of improving the aesthetics of your engine bay. A freshly washed, shiny, black engine tends to look better to many people than one that is dull looking.

Some car owners get a distinct impression that if something looks pretty, it is automatically working better. While this is certainly true of some mechanical components, and while there are plenty of benefits to washing and waxing your vehicle in general, engines don’t usually need to be washed frequently to operate well.

This is because modern engines are encased in quite a bit of hard plastic which helps shield them from the effects of materials such as dust or pollen and helps keep the engine safer from inclement weather and damage.

The hood of your vehicle also goes a long way in protecting the engine bay from moisture, damage, dust, and wear and tear. Some car owners, though, feel that a beautiful, shiny engine is an important part of the look of their vehicle. If you do want to wash your engine, there are some safe and gentle ways to accomplish this.

Can You Safely Wash Your Engine with Water?

Yes, there are steps you can take to safely and carefully wash your engine. To start

  • Turn off your vehicle and allow the engine to cool down fully on its own
  • Open the hood
  • Remove the air intake filter and set it aside in a dry, clean place
  • Cover any electrical components with plastic bags to shield them from water
  • Gently wet the engine and lather using warm soapy water and a cloth
  • Rinse the engine carefully once the soap has been allowed to sit
  • Keep the water for rinsing localized, and use a moderate spray or pouring radius
  • Allow the engine and bay area to dry completely before re-installing the air intake filter, uncovering electrical components, and closing the hood

The most important thing to remember here is to make sure that your engine has fully cooled down before washing it. Don’t try to speed up the cooling process with cool water. Protect any electrical components and remove parts that could be damaged or compromised by water.

Keep the application of water and soap localized to the engine itself. This will help you avoid getting water or soap anywhere it doesn’t need to be and keeps moisture away from delicate components.

You can choose to towel the engine dry or allow it to air dry. Either way, don’t forget to re-install your filter or any other parts that have been removed for safety reasons.

Car detailing manual car washing the engine with pressure water close up

Pressure Washing Can Be Risky

One thing you’ll want to avoid doing to an engine (or to any part of your engine bay) is pressure washing it. While some car owners swear by the rapid results and shiny look, using such high levels of water pressure can knock things loose, cause damage, and compromise the safety of your vehicle.

Pressure washing sprays water at such high levels that water can force its way into sensitive electronic parts as well as into the engine itself. Pressurized water can be strong enough to penetrate parts susceptible to corrosion and cause major damage down the road.

Use a Gentle Soap or Degreaser

One thing to keep in mind is that your engine will work best with a gentle degreaser, and not with any old cleaner.

Certain chemicals or products may promise cleanliness, but they may not be safe for your engine. Using a mild soap or a basic degreaser will be sufficient. A lot of the products on the shelves are meant for heavy-duty restoration or cleaning vehicles that have been parked in a garage for years.

If you’re just freshening up the look of your engine, simple materials will do. You’ll save money and may help protect the other more sensitive parts of the engine bay from harsh or corrosive chemicals.

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Super Clean - Multi-Surface All-Purpose Gunk Remover Aerosol Degreaser

Frequently Asked Questions (FAQ)

Q: Can I Use a Garden Hose to Wash My Engine?

A: A garden hose or low to moderate pressure can be used on an engine, so long as the water is kept confined to the engine and the intensity of the water is reasonable. We personally and professionally recommend a rag and a bucket over a hose, but if you’re careful with your garden hose, everything should be fine.

Q: Can Brushes Be Used on Engines?

A: You can use either a rag or a brush to clean your engine. Using a rag or a brush with a gentle degreaser will yield careful, beautiful, and precise results that can help keep chemicals localized, and away from other engine bay parts.

Q: How Long Does It Take to Air Dry My Engine Bay?

A: It should take half an hour to an hour for your engine bay to fully dry out. Less time if the weather is hot, sunny, and dry, and you’ve got the car parked outside. Feel free to use a dry rag or towel to help dry your engine, too.

Q: Are there any benefits besides cosmetic appeal to washing my car engine?

A: Sometimes. If your engine bay is especially dusty or dull looking, a moderate amount of water can help loosen up and wash away dust and other particles which can impact vehicle performance. Most vehicles don’t need to have the engine washed often if at all, but if you live in an especially dusty or pollen-heavy environment, it can help keep the engine bay healthier and cleaner.


Washing your engine is a job best taken on using mild to moderate water pressure, hand washing, and some basic cleaners. Failing to keep these factors in mind could lead to damage to electrical components or the alternator, water getting into your engine, or damage to the engine if you don’t allow it to cool down on its own. 

Never try to cool a hot engine with cool or cold water and avoid pressure washers to make sure your engine bay electronics and hardware is kept in their best working condition. Using a mild soap or basic degreaser on your engine is best and washing by hand will give you the most precise results.

Remember to let your engine cool down fully on its own, remove the air filter and store it in a safe, dry place, and cover all electrical components before you begin to wash your engine. After washing, allow the engine to air dry, or towel down.

Replace the air filter, uncover your electronic connections, and close the hood. Your engine is now clean and looks great while keeping the rest of your engine bay safe and usable.

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Motor Hills


Super Clean – Multi-Surface All-Purpose Gunk Remover Aerosol Degreaser

Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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