Coolant Fouled Spark Plug: Is It Bad and What to Do? (Fix)

While a coolant works wonders in regulating the temperature, it can cause significant problems if it leaks in areas it’s not intended to reach. Since a coolant works near the engine, you may wonder what will happen if it leaks and reaches the spark plug. Thus, you may ask:

If you have a coolant-fouled spark plug, is it bad? And what should you do with it if it ever happens to you? If you have a coolant-fouled spark plug, it can cause significant problems that can lead to an engine misfire and even internal damage. The leading cause of these kinds of problems is a leaking head gasket or intake manifold. In general, it can damage a spark plug, wearing it out quickly than how it should.

If you’re not aware of this problem, coolant fouling might be frightening. However, all you need is a correct answer, and you’ll be OK. On the other side, ignoring it may cause you to have more significant issues down the road.

In this post, you’ll learn all there is to know about a coolant-fouling spark plug and what occurs when it happens. This way, if it occurs to you, you’ll learn how to deal with it. It can also assist you in preparing for it and preventing it from occurring.

Without further ado, let’s get into it!

Coolant Fouled Spark Plug

Is It Normal to Have Coolant on Spark Plugs?

No, it’s not normal to have coolant on spark plugs. Coolants work by regulating the temperature, and the substance should remain in the radiator where it belongs.

Thus, if the internal coolant leaks and reaches the spark plug, it can cause significant damage that’s enough to misfire an engine.

If the coolant burns, it will leave deposits or particles on the spark plug’s insulators and electrodes. These particles can create hot areas that can ignite and misfire a code.

You can tell if you have a coolant on spark plugs if you see a chalky appearance in the plug after pulling it out.

What Happens When Coolant Leaks Into the Spark Plugs?

When a coolant leaks into the spark plugs, it can cause significant problems and damages that can wear the whole engine down.

For instance, a coolant that leaks can reach the head gasket outside the engine. It can even reach both the combustion chambers and the cylinder.

For this reason, you can notice it leaking between the engine head and block. Once the engine turns off, it will then reach the cylinder.

Such leakages open a lot of risks for the health of your engine. Thus, once it reaches the spark plugs, you’ll want to address it soon, or it will cause damage to the spark plugs as well.

Can I Drive With Coolant in My Spark Plugs?

Like all other substances that can leak in your engine and reach the spark plugs, a coolant will less likely disable your engine. In short, you can still drive even with coolant in your spark plugs. However, it’s not ideal for you to do so.

Since a coolant in a spark plug can cause misfires, it can harm your engine more if you keep on running it despite the warnings of misfires.

In general, having a coolant in the combustion space and the spark plug causes many problems. For instance, it can cause poor performance on your engine and foul your spark plugs, wearing it quicker than usual. 

If left unchecked, a coolant in spark plugs can wear down your engine and cause significant damage in the long run. Thus, if you think you have coolant in your spark plugs, it would be best to stop your engine and have it fixed.

coolant on spark plug

Can Coolant in Spark Plugs Cause a Misfire?

Yes, having a coolant in spark plugs can cause a misfire. A leaky combustion chamber or head gaskets might be the root cause of the problem, and the fouled spark plug could be isolated to one or two nearby pistons.

In most cases, it also implies that drivers will continue to drive a car with a coolant leak for thousands of miles as the plug gradually fouls. 

Previously, if the converter became blocked, the engine would shut down before any serious harm was done.

Coolant Fouled Spark Plugs Symptoms

If you want to know if your coolant fouled your spark plugs, you can always check your vehicle for its symptoms. Here are five significant symptoms you can see in your vehicle if you have a coolant-fouled spark plug:

Engine misfires

Internal coolant failures can lead to a misfire by fouling the spark plug. A leaky intake manifold or a cylinder cap might be the source of the problem, and the contaminated plug could be isolated to one or two adjacent cylinders.

Deposits or particles in the electrodes and insulator

The burnt coolant creates deposits on the conductors and insulation, potentially causing pre-ignition and setting a misfire code.

Chalky appearance on electrodes

The ground strap and center electrode may have a powdery look when the plug is removed. Due to the decrease of phosphate, zinc, and other chemicals that can taint catalytic converters, newer coolants do not create this sort of accumulation as rapidly.

Clogging in the engine

Unfortunately, this implies that drivers will continue to drive a car with a coolant leak for thousands of miles as the plug gradually fouls. Previously, if the converter became blocked, the engine would shut down before substantial harm was done.

Damage to other parts

Pollution of the coolant might cause the bearings to fail. In addition, a coolant passing via the combustion chamber can potentially contaminate the catalytic converter and the oxygen sensor.

Coolant Fouled Spark Plug Fix

If you have a coolant-fouled spark plug, you need to have it fixed as soon as possible. While you can get someone to do it for you, you can permanently repair yourself. 

If you want to save some money for such simple repairs, you can follow these quick steps on fixing a coolant-fouled spark plug:

Scrape the electrode with sandpaper.

A tiny bit of metal protruding from the end of the spark plug (on the side that enters the engine) can be found. If the electrode is dark or tarnished, rub the sandpaper back and forth through the bent-over part of the electrode and the spark plug itself until you see precise steel on both sides.

The spark plug electrode should have a bare metal appearance. If it doesn’t, sand it some more until it does. When sanding, always use safety glasses and a mask.

If the electrode is highly filthy, use a file to remove it.

If sandpaper doesn’t work, change the spark plug. However, if you’re in a hurry, a tiny file can be used to scrape away substantial carbon accumulation on the electrode. To wash the metal, insert the tool into the space between the plug and the wire and push it back and forth.

Scrape the threads using a wire brush.

There’s a strong chance that oil and filth have built up in the threads of your spark plug, making re-installation difficult. To remove the bulk of the built-up muck, scrub the threads with your wire brush at a perpendicular angle to the spark plug. 

This way, the brush moves in the same direction as the plug’s threads. Then move to another viewpoint and scrape it for maximum impact.

To avoid being poked by the wire brush, use protective gear while doing this. The threads don’t have to be spotless to work, but they should be clear of most accumulation.

Clean the plug with brake cleaner and a soft cloth.

Brake cleaner is available in spray cans at your nearest auto repair shop and can be used to remove dirt from various vehicle components. In addition to cleaning, it evaporates fast, allowing the components to dry quickly. Apply brake cleaner to the plug and threads, then wipe off any residual dirt particles using a clean towel.

If your spark plugs are very filthy, use the brake cleaner and the scrubbing brush to remove the trapped dirt.

After removing all brake cleaners that have absorbed oil and dirt, wash the plug down entirely with the towel.

Carry on with the procedure for every spark plug.

Reinstall the first spark plug and reconnect the spark plug cable to it once it has been cleaned. Then continue with each one until all have been cleaned and replaced.


In a nutshell, you can conclude that a coolant-fouled spark plug means an issue that needs a solution as soon as possible. If your spark plug is clogged with coolant, it can create serious difficulties, including engine misfire and even internal damage. A leaky head gasket or intake manifold is the most common source of these issues. In addition, it can harm a spark plug in general, causing it to wear out faster than it should.

While the best thing is to get an expert to do it, you can save some money by fixing it yourself. It’s a simple process, but it helps in maintaining your spark plug and your engine overall.



Image credits – Canva

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My name is Hank, and I've been in the automotive industry for 27 years. I've been working in my own auto repair shop for the last 13 years, and now I want to help you here, on my blog. Let me know if you have any questions. Read more