Cleaning your car engine at a self-serve car wash can be risky. High-pressure water can force moisture into sensitive electrical components, which may lead to malfunction. If you choose to clean your engine there, ensure the engine is cool, cover sensitive areas like the distributor and electrical connections, and use a low-pressure setting. It’s often safer to use a professional service or clean it manually with a gentle approach.

Use a low-pressure spray to rinse the engine bay. This shouldn't be a problem at home, but self-serve car wash water guns have high water-pressure capabilities. You must be careful when using them and never pull the trigger to engage high pressure when cleaning your engine bay.

Most carwashes have a separate area for cleaning engines and they will use a different set of cleaners and tools than they use for washing the exterior of the car. After the engine is cleaned, the carwash attendant will likely blow out any leftover water from the engine bay with compressed air.

In addition to the advantages, washing the engine may also have some disadvantages, including: moisture in the ignition device, which results in starting problems, moisture in air filters, damaging electrical and electronic components located in the immediate vicinity of the engine.

Especially engines. If you're cleaning a car that's above 2003, you can assume that most of the wires are water sealed with only a few parts that you'll need to cover up like the alternator, intake, battery, etc…

Preparing Your Engine for a Wash

Washing an engine isn’t like washing the exterior of a car, where a high-power spray of water and good, soapy scrub go a long way. Because of the many different working parts in an engine, you should be less concerned with blasting every nook and cranny and more concerned with knocking loose and gently spraying away the largest accumulations of dust and grit.

Your car doesn’t have to be cooled down to wash the engine, but you don’t want to introduce cold water directly onto a hot engine, so time your wash carefully. Make the car wash is your first stop of the day or, if you’ve been sitting in hot traffic for a while, park to the side and give your engine a chance to cool before you start the wash.

Some people prefer to apply an engine degreaser before they wash, as this will help eliminate the buildup that accumulates over the years. If you regularly wash your engine, however, this step won’t be as important.