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What Is Carbon Fouling And How Do I Fix It?

Educational  ·  May 13, 2021

What Is Carbon Fouling And How Do I Fix It?

Spark plugs spend their entire functional life inside the combustion chambers of your engine. There, it’s exposed to fuel, air, and constant explosions that it triggers by causing a spark (hence the name). Over time, though, spark plugs can experience carbon fouling and become less useful.

Carbon fouling happens when the car’s air and fuel mixture is too rich, which means the proportion of fuel is too high. It results in incomplete combustion, leaving behind a carbon buildup on the spark plug’s firing end. Simply put, carbon fouling is a symptom of a fuel problem, not a spark plug problem. You may use sandblasting to remove that buildup of carbon, but it does not solve the root of the problem.

In this article, we’re going to take a deep dive into the issue of carbon fouling on your spark plugs. We’ll explore what it is, what causes it, and what symptoms to look out for to know if your plugs are suffering from carbon fouling. Lastly, we’ll look at how it’s typically fixed and how you can prevent it from happening again in the future.

Let’s get started.

What Is Carbon Fouling?

By definition, 'fouling' is when something unwanted accumulates on a hard surface. In the context of carbon fouling on spark plugs, it refers to excessive fuel carbon that accumulates on the spark plug electrode. This buildup has gotten to the point where the plug can no longer generate the sparks needed for efficient combustion.

If you remove the individual spark plugs and inspect them up close, what you’ll see is a grey or black matter all over the spark plug’s electrode and porcelain. That matte coating is the carbon buildup.

Other Types of Fouling on Spark Plugs

Here’s the thing: there are also a couple of other ways that your spark plugs can get fouled besides carbon from fuel. They are:

What Causes Carbon Fouling on a Spark Plug?

Carbon fouling on a spark plug is caused by a problem with the fuel that you use. Often, we describe it as a fuel mixture that's too rich, which means that the ratio of fuel to air is far too high.

That can cause combustion problems, resulting in excess carbon that sticks very quickly to the hot parts of the spark plugs.

Again, we must remember that carbon fouling (or any other type of fouling, for that matter) is only a symptom and not the root problem. So, if you know that you're experiencing carbon fouling, you must troubleshoot and resolve whatever issue causes it.

If not, any new spark plugs that you place in your engine will just get fouled up all over again.

Other Less-Known Causes of Carbon Fouling

Whenever you read or talk about the causes of carbon fouling, the first answer you’ll always get is that the fuel mixture is far too rich. That’s still true, but here are a few other possible reasons behind carbon fouling:

What Are the Signs of Carbon-Fouled Spark Plugs?

The most effective way to diagnose your spark plugs is to take them out and inspect them with your own two eyes. As mentioned before, carbon fouling will appear as a grey or matte black finish on the spark plug’s electrode and porcelain.

Still, there are some other tell-tale performance symptoms that you can look out for before you choose to do that. They include:

Sure, those symptoms can point to a long list of different problems under the hood. However, it might help to inspect your spark plugs first and rule out carbon fouling.

Can You Clean a Carbon-Fouled Spark Plug?

Yes, it’s possible to clean a carbon-fouled spark plug instead of replacing it entirely. Some of the methods used are:

Sandblasting – Using a machine that shoots sand out with a jet of air to scrape the carbon off the spark plugs

Burning with a butane torch – Some DIY repairers have also shared that it’s possible to burn off the excess carbon with a butane torch

Using wire brush or sandpaper – To scrape off the carbon manually

Applying spark plug cleaner – Some products on the market can help you keep your spark plugs clean. These generally don’t cost too much, and you can find them at your preferred auto parts store.

How Do You Prevent Carbon Fouling?

The most important thing you need to remember is that carbon fouling is a symptom and not the root cause. So, suppose it has already happened, but you haven’t solved the main issue; it only means that you will experience it again and again until you solve the main issue.

Here are some preventative measures you can take to protect your spark plugs from carbon fouling:

Besides that, you may consult your mechanic, the seller you're buying your plugs from, or even your car manufacturer. Your vehicle’s User Manual might also have recommendations on what spark plugs you should use.

Be a Smart Car Owner! Learn from CarPartAU!

To learn more about issues like carbon fouling and spark plugs, head on over to the blog at There, you’ll have access to plenty of free articles teaching you about auto maintenance to help you become a better-informed car owner!

By Ray Hasbollah

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