Skip to Content

Wash My Car When it’s Running? Not advisable, here’s why…

A car is one of the most expensive possessions we’ll own in our lifetime. It’s no surprise then that we want to protect, clean, and make it presentable. A car is more than a car, it is an extension of our personality and speaks volumes to other people about who we are and how we conduct ourselves in the world.

While you can wash your car while the engine is running, doing so is not advisable. There’s no risk to the car, but there is a risk to your health. Washing your car thoroughly will require getting up close and personal and while washing the rear of your vehicle you’ll be exposed to poisonous carbon dioxide from the tailpipe.

In this post, you’ll learn why I don’t advise washing your car with the engine running. You’ll also learn why I don’t like engine washing. As a mechanic with twenty-five years of experience, I’ve seen a ton of expensive engine washing mistakes, I’ll show you how to avoid all of them.

Hand car wash at home

Washing While Running

Cars are not completely waterproof but they are weatherproof and capable of driving through all types of adverse weather conditions.

So what’s the difference between waterproof and weatherproof?

Waterproof – Wading a car through a deep puddle obviously should be avoided, but approached correctly it doesn’t usually present a huge issue so long as the car doesn’t ingest water and the car doesn’t spend too long in the water. Most cars will travel through water about 15 – 30 cm, after that the car starts to float and you become a passenger.

But the real problem is, cars that remain in deep water for a prolonged period, develop leaks. Water starts to leak in between metal panels, areas that aren’t designed to keep water out.

Weatherproof – Cars are however designed to be weatherproof, meaning they have been designed to withstand driving rain over the panels, and the use of engine splash covers keeps the road splash off the engine components.

Washing an Idling Car is a Safety Hazard

Your car will have no trouble idling while being washed, you won’t cause an issue to the engine or the electrics. Directing high-pressure water around closings like doors, hood, trunk lid, sunroof, and window seals do increase the risk of a small water leak. But you already know modern cars are pretty well sewed up when it comes to rain and wind.

The hazard with washing a car while it’s running is to you or the wash attendant. Carbon dioxide from your car’s tailpipe is carcinogenic and is especially dangerous in confined spaces like a garage etc.

Washing a car thoroughly will mean getting intimate with the body panels and that places you very close to the tailpipe so you can see the risk.

A good trade-off here would be to wash the rear of the car first with the motor off and then start the motor if you must.

Best Way To Wash Your Car

Depending on your time constraints, opt for any of the following methods.

Automatic Car Wash

The most widely known method of getting your car washed. Available next to most large gas stations, the automatic car wash is the quickest and simplest way to clean your car.

Most auto detailers will however look at automatic car washes with disdain. The old-school versions used hard bristles that could leave tiny scratches throughout the car. The updated versions use a softer cloth material. However, these soft clothes tend to hold on to the grit and grime of the previous car, possibly subjecting your car to scatches as well.

Finally, there are touchless car washes that do not use any brushes but instead rely on high-pressure water jets. Many claim that these provide a sub-par experience as some grime simply requires physical contact to be scrubbed off. Additionally, these types of washes tend to use harsher chemicals to compensate for the lack of brushes.

In the end, if you ask an auto detailer about automatic car washes, they’ll say to stay away. However, if you are driving a regular car your paint will be fine, but your car probably won’t be 100% clean.

Self-Service Car Wash

This type of car wash will require more effort on your part. It’s a perfect compromise if you don’t have any cleaning supplies at home, but have some stubborn spots that need to be cleaned.

Typically these locations have individual stalls with a pressure washer and a large brush. The pressure washer will typically have a choice of different cleaning detergents that you can select from. The benefit of course to this type of wash compared to the automatic car wash is that you will be able to focus on specific areas of your car.

If there’s a particularly dirty spot on your exterior, such as under the fenders you can hone in on it until it’s spic and span. The con of this method is that you will have to do it yourself.

Hand Wash At Home

For some, cleaning their car is almost therapeutic. Regardless of the reasoning, washing your car yourself allows for the most flexibility and control. It’s a pricier option initially, but most cleaning products will last a very long time.

It’s best to avoid washing your car with standard household cleaning products. Those products are most likely too harsh for your vehicle’s paint. Instead, find auto-specific cleaning supplies for best results. Sometimes you’ll encounter stubborn areas that will require the use of a harsher bug and tar remover.

When it comes to sponges, it’s not recommended to go in a circular motion as this can cause noticeable swirl marks. Instead, it’s advised to go with long strokes along the length of the body panel. Additionally, have separate sponges for the body and wheels. The wheels will have a larger amount of sand and dirt attached to them that will cause scratches to the body if the same sponge is used.

Top Tip – use a professional detailers bucket, it contains a grit guard at the bottom which is crucial for preventing swirl marks. You can check it out here on the “Car cleaning tools page”, it’s part of the Chemical guys kit.

Should You Wash Your Engine?

Engine car wash

A combustion engine is unfortunately a messy place. Oil leaks, grease, fumes, road grime, dust all contribute to the condition of the engine bay. The engine bay is a rarely seen part of the car, that’s not to say it shouldn’t look its best. An owner understandably wants the engine bay to shine, but the question is should you wash it?

You should not wash under the hood of your car. Doing so risks serious component damage. Modern cars employ multiple control modules and components that employ sensors. While these components are weatherproof, the high pressure associated with pressure washing could penetrate the electrical component’s weather pack seals, causing the circuit to short out or worse control module failure.


There are plenty of stories of people deciding to wash their engine and then met with a flurry of check engine lights and no start.

It’s advisable to steer clear of power washing under the hood, the risk is too great, and the cost associated with module replacement is measured in thousands as they must be new modules, used modules won’t work.

How To Clean Your Engine?

If you do decide to clean your engine, it’s a simple process. It’s recommended to turn off the car before cleaning and allow it cool. We won’t be using a pressure washer, so you can put it away. To clean under the hood we’ll be using an engine degreaser, it’s a special foam solution designed for the job.

We’ll finish the job by coating the engine bay with a coat of engine protector.

Before we go at it, I’ll share the don’ts of engine cleaning:

  • Don’t use a pressure washer
  • Don’t use a garden hose
  • Avoid water on the alternator
  • Don’t wash the drive belt (serpentine belt)
  • Avoid water on coil packs
  • Avoid water on fuse boxes
  • Avoid water on control modules
  • Don’t clean a hot engine
  • Don’t use a flammable cleaner such as gas, diesel, kero, etc.

Tools you’ll need are as follows:

  • One can of Gunk engine degreaser
  • Selection of scrubbing brushes
  • Shop towels
  • One can of Gunk engine protector

Check out the Gunk engine cleaner here on

Check out the Gunk engine protector here on

Compressed air would be nice, a vacuum cleaner works too.

We’ll need to use some elbow grease also, and the finished result won’t be as clean as a freshly built engine off the assembly line, but it will look a hell of a lot better but more importantly, it’s a safe way to clean your engine bay.

The process looks like this:

  • Turn the engine off and allow cool a while – A cool engine with no moving parts is a safer environment when working in the engine bay.
  • Remove plastic engine covers that are easily removed, they may be cleaned off the vehicle if easiest.
  • Use vacuum or compressed air to remove leaves pine needles etc from windshield cowl and nooks and crannies of the bay
  • Spray engine gunk on engine and chassis but avoid – drive belt, alternator, coil packs, control modules
  • Use various brushes to agitate the dirt
  • Use shop towels to remove the grime
  • Allow dry before spraying the bay with the engine proctor
  • Now stand back and admire your work

Will Cleaning The Engine Improve Performance?

While cleaning the internal components of an engine, such as fuel injectors, or cleaning the air filter will improve performance, cleaning down the exterior of the motor will not.

That said, there are a ton of good reasons to keep your engine bay clean:

  • It helps you or your technician when it comes time for an inspection
  • Spot issues such as leaks et., sooner
  • A clean engine bay is easier and nicer to work on
  • A clean engine bay is safer to work on
  • Less likely to lose fasteners or tools

You may find the following posts helpful:

How do dealers make cars so shiny?

Does rain ruin a car wash?

Are Weathertech worth it?

Are car seat covers worth it?

Can you take a soft-top through a carwash?