What to avoid when washing the engine? This is perhaps the first question you should ask yourself if you’ve decided to do this job.

Washing the engine has always been and is one of the more favorite DIY jobs.

But the fact is that this job doesn’t go under regular car cleaning.

It demands more caution and the truth is that one careless move may cause lots of costly problems.

To be clear, this article has no intention of talking you out of it, on the contrary.

Rather, it should give you some guidelines on what to avoid when washing the engine and how to do the job more safely.

If you want to read more information about washing the engine and engine bay, click here to read a separate article on that topic.

You can also watch a related video at the end of the article or on our YouTube channel.



Before we start with the tips, I would like to underline one important thing:

The engine bay is not a regular part of the car for cleaning, like the car interior for instance.

You can’t just grab a cloth and cleaner or a pressure washer and systematically start rubbing, washing, and cleaning.

The engine bay (especially in today’s cars) is packed with sensitive components (electric and electronic especially) that are very sensitive to water and impact.

This is why you must be careful when cleaning and make certain preparations. For instance, a drop of water in the wrong place can cause big and costly problems.

All of this goes double for older and high-milage cars. Here lots of the components, over the years, become more brittle and sensitive than they usually would be (things like connectors, hoses, and else).

Have this in mind before you start.

Also, these tips apply to washing the whole engine bay not only the engine. When you start washing the engine all of the other components and systems under the hood will also be affected.

Now, back to the point and the tips for what to avoid when washing the engine:



A very popular tool for cleaning the engine bay is a pressure washer. Yes, the results are good but if the pressure is too strong, it can easily damage things like small hoses, various plastic parts, connectors, wiring, and else.

Even worse, it can force water into parts that are otherwise well protected. Electronic components are especially sensitive to this (fuse boxes, connectors, various housings, etc).

Perhaps use a setting with lower pressure and with a weaker jet of water. It’s safer although maybe less effective but try to compensate this with more rubbing or a better cleaner.



When using the pressure washer, avoid keeping the water jet in one place for a longer period of time.

This can easily cause a flood and water can easily enter places where you don’t want it.

This is also applicable if you’re using a hose. Try to always use a sprinkler or mist setting instead of a splash or stream.

Again, when mentioning what to avoid when washing the engine, electric and electronic components are the most sensitive.

So, when spraying with water, use the correct setting and don’t hurry too much but don’t be slow either. A fairly quick pass is the best.



You can’t clean the engine properly and get the best results without using some sort of cleaning substances.

The most important tip on this part would be to buy cleaners made specifically for this task.

Various homemade recipes and household cleaners are popular and cheap but can easily damage some parts of the engine and engine bay.

So, when buying, ask specifically for an engine cleaner. Also, be careful where you apply it. You don’t have to spray it everywhere, just on parts that are greasy and filthy.

Again, especially avoid soaking electric and electronic components.

One more thing when talking about what to avoid when washing the engine. Make sure to flush out the cleaner as much as you can so there’s nothing left over.




Disconnecting the battery is something that I highly recommend when washing the engine, although lots of people don’t do it.

The rule and truth are that water and electricity in the same vicinity are not a good idea.

There’s always a serious risk of causing an accidental short circuit for instance which can cause further huge problems, even like damaging the ECU.

To avoid this possibility, best take off the minus battery clamp. Do this especially if the battery is exposed and the terminals are directly in contact with water.

If the battery has its own plastic casing then there’s a much lower chance of this happening. But even then if you want to be a hundred percent safe, take the minus battery clamp off.

So, what to avoid when washing the engine? Washing with the battery connected.

If you don’t know how to remove a battery terminal, click here to take a look at this article we’ve made. It’s about replacing the car battery where you can find, among other things how to take off the battery clamp.




Before you start, be sure to protect the parts of the engine and engine bay that are exposed to water and where they might be damaged.

Do this especially if you’re going to remove certain parts to get better cleaning results. For instance, removing the engine cover is a good example.

On most cars, once you remove it, certain parts might be left open and exposed (like the throttle body, parts of the air intake system, connectors, and else).

You don’t have to go overboard with protection. In most cases, just putting a simple plastic bag or a piece of cloth over the exposed places will save the day.

By doing this, you’ll seriously reduce the risk of getting into trouble and you’ll protect the vital components of the car.



Among all of these tips for what to avoid when washing the engine is one that’s perhaps the most important:

Be always aware of what you’re doing when washing and cleaning. Especially if you decide to use a pressure washer or aggressive cleaners. I can’t emphasize this enough as most problems come from recklessness and lack of knowledge.

This rule goes double and triple for modern, oftentimes crammed engine bays. Doing a lot of careless cleaning can easily lead to damaging certain components. Not only is this costly to repair in most cases but it may be hard to reach and demand some serious dismantling and labor.

If you face an engine bay like this one, better do less detailing than cause yourself a ton of trouble.

Once more, stay away from fuse boxes, electric or electronic housings, connectors, and else as these are the most sensitive to water and moist.

Also, if you drive a high-tech, expensive car I would seriously advise against washing the engine or engine bay on your own. Yes, it’s doable, but it’s very risky, at least in my opinion.

In the end, a clean engine and engine bay are a pretty sight, that’s the truth. But not at all cost and not if you’re going to have headaches later.



Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com