How to Wash a Car Engine at the Carwash

As a quick experiment, I talked to a dozen friends and family members who I would classify as “car knowledgeable,” i.e., not car nuts but certainly not clueless.  They can check their oil, change air filters and are up to speed on basic maintenance.

None of them had ever washed their car engine.  Not one!  This includes a guy with 300K miles on his Cummins diesel.  That’s unfortunate because a clean engine offers mechanical as well as cosmetic benefits.

Here’s my rule of thumb.  Wash your car when it’s dirty.  Clean the interior every 3-4 months.  As far as your engine goes, wash it at least once a year and possibly more depending on where and how you drive.

So, for all you DIY types with dirty engines, let’s jump into how to wash a car engine at the carwash or at home.

It’s simple, fast and doesn’t cost an arm and a leg.

Why Wash Your Car Engine?

The short answer is most people do it for cosmetic reasons, but there are a few mechanical reasons as well.

First, a clean engine makes it easier to spot problems such as oil or other fluids leaking.  A lot of modern cars have black panels and components.  Couple that color with the natural buildup of dirt and grime, and it becomes really difficult to spot problems.

Secondly, having a clean engine means less accumulated dirt and grime to penetrate interior engine parts such as air and cabin filters. Also, some buildup can be corrosive or flammable depending on the material.

Lastly, it makes routine monitoring and maintenance easier.  People are more likely to check their fluid levels and belts, for example, if they won’t get their clothes and hands dirty.

As far as the cosmetics are concerned, it should go without saying that if you are considering selling or trading in your car, wash the engine!

Three Considerations Before You Start

  1. Is your car old or new?
  2. Does your car wash have a low pressure setting?
  3. What are safety concerns?

New cars, say 2000 onward, are generally well protected.  They usually have plastic engine covers, and all connectors have plastic or rubber coatings.

For newer cars, just be careful around the fuse box, alternator (cover with plastic if needed) and any electrical areas that look exposed. If you have an older car, cover the alternator, carburetor and distributor with plastic bags and secure with tape or rubber bands.

High-pressure sprayers can dislodge parts and connections as well as force water into sensitive parts of the engine.  Be sure you have a low-pressure hose or sprayer available.

As far as risks go, professionals suggest that batteries be covered with plastic bags or the negative terminal cable be disconnected.  While this can be a bit of a hassle, it is a safety procedure that helps prevent unwanted electrical currents.

The 5-Step Process For Washing Your Car’s Engine

Step 1:  Remove all visible debris

Leaves and dead bugs are found in almost every engine.  Vent openings, grills and battery boxes are just some of the debris magnets you have to deal with.

Basically, you have three options here – vacuums, hand brushes and compressed air or leaf blowers.  Most debris can be removed with a hand cloth, but for my car, there are a few nooks and crannies where only compressed air works.

Step 2:  Degrease the engine

Most cars are dirty enough that they require degreaser to loosen up oil and grease before washing.  Kitchen soap, even Dawn, is rarely sufficient.

Start your car and allow it to run for 5 or so minutes.  A slightly warm (not hot!) engine makes the degreaser more effective.

If you are doing this at home, put a drip pan, piece of cardboard, etc., underneath the car to catch any excess cleaner and oil/grease runoff.

Degreasers come in water base, citrus base, solvent base, gel, foam and spray bottles.  They all have tradeoffs.  Solvent base is better for really dirty engines but can harm paint if accidentally splashed.  Water base and citrus base are gentler.  Foam and gel stick to the sides better and don’t drip.

Read the labels and choose the best for your situation.  I personally prefer Chemical Guys Signature Series (citrus base) for routine jobs and Meguiar’s Super Degreaser for heavier duty jobs.

Apply the degreaser starting at the bottom and work your way to the top.  This won’t get your engine cleaner, but it will keep YOU cleaner.

For areas that have a lot of buildup, use a brush or cloth to break up large deposits.  Keep a cloth hand to quickly remove any degreaser that splashes on to the paint.

Always follow the instructions for whatever degreaser you purchase, but most products recommend 3-5 minutes of soak time.

Step 3:  Wash the engine 

This step is pretty simple.  Don’t use a high pressure hose and avoid sensitive areas (e.g., alternators) as much as possible.  Most car washes have both high and low pressure settings, so be sure to check first.

If you are washing your engine at home, a garden hose can work, but a purpose-made pump sprayer is preferred.

Step 4:  Dry the engine

The same rules for washing cars apply to engines.  Never “air dry” as it will leave water spots and undo much of your hard work.

Wipe down the engine with hand cloths or use an air compressor or leaf blower to get rid of excess water.  Once this is done, turn on your car and let if run for 5 minutes to dry interior components.

If you simply want a clean engine, you can stop here.  If you’re going for a showroom floor look, proceed to Step 5 to learn about engine polish.

Step 5: Make it shine

While your engine is now clean, the plastic parts likely have a dull “matte” look to them.  Not to worry.  There are several really good engine bay dressing products available.

Simply spray on all surfaces that you want to shine.  Let it sit for 30 minutes to 1 hour and wipe off with a microfiber cloth.  Griot’s Engine Bay Dressing worked well for me.

Not only does this make your engine look new, it also provides an extra layer of protectant between your engine and future oil and grease buildup, thus making future cleanings easier.


Knowing how to wash a car engine at the carwash or at home will save you money AND extend the life of your car.  Plus, for DIY types you get the added satisfaction of a job well done.

That’s definitely worth a few bucks and 1-2 hours every year.



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