How to tell if a spark plug is bad by looking at it

Did you know you can determine a spark plug’s condition just by looking at it? Not all the time you have to face symptoms from bad spark plugs’, as their outlook will tell a lot about their condition.

How To Tell If A Spark Plug Is Bad

As a part of the inspection process, how will we know if the spark plugs have gone bad or not? That’s what we are going to share today in this article. To learn more, have a glance at it!

The 6 outlook of a bad spark plug

Outlook Of A Bad Spark Plug

1. Carbon deposits

If you notice foul carbon deposits caked on the spark plug, know that there was improper handling of the air-fuel mixture, dirty air carburetors, or frequent idling of the engine.

These issues arise only when the spark plugs are malfunctioning, and fuel is getting stuck on the tips.

2. Oily insulator tips

When the oil cylinder of the spark plugs leaks, the oil gets clogged up onto the insulator tips and on electrodes.

Oil deposits and carbon deposits look almost the same, but the texture is different. If the oil freezes in those places, the spark plug may not work correctly.

3. Burnt

Have you seen white blisters on the spark plugs’ insulator tips? Then those arose as the spark plugs got too hot and burned.

Specific factors get overheated; one includes loose spark plug or improper handling of air/ fuel ignition.

4. Wet

While you notice the spark plugs are wet, then know it happened due to engine flooding. Engine flooding occurs when you keep restarting the engine without letting it fire up. If the dampness is not dried, then it will corrode the components.

5. Broken

If you notice the broken spark plug’s electrodes, then it is your fault for choosing the wrong type for your vehicle. Too short spark plugs cannot cover the required mileage.

Hence the electrodes break, handling that much pressure. In this case, the spark plugs need replacement.

6. Worn electrodes

When the spark plug seems worn out, it is time to replace it as it has reached its last stage of life. A worn-out spark plug will not provide optimum power to the engine.

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The 3 Reasons why spark plugs look bad

Reasons Why Spark Plugs Look Bad

#1. Improper placement:

One of the reasons why spark plugs start looking bad is the lack of installation knowledge. If the placement of spark plugs are too far away, they start overheating.

For this, the components get burned soon. Also, not knowing choosing the right size spark damages their performance and outlook.

Too long ones can cause engine damage, and too short ones can hamper gas mileage, making your spark plugs break soon out of pressure.

#2. Lack of care:

Examining the spark plugs as routine maintenance is crucial. Even if you do nothing, just looking at the spark plugs can save them, whether they are okay or not.

If you see some damage is peaking, then you can immediately take action. Or else, after several months, those damages intensify, and the plugs die.

#3. Driving the car too slow frequently:

When you drive your car at a low speed more often, the air-fuel mixture cannot burn properly. Hence, day-after-day, the plugs get carbon-fouled.


Cleaning method of a bad looking spark plug

Cleaning Method Of A Bad Looking Spark Plug

To clean the debris, oil, or carbon on your spark plugs, you just need a wire brush and brake cleaner. Spray the cleaner, sit for a few seconds and brush the debris off. If you know the right installation method, then you can dismantle the plugs for a deep clean.


How does a regular spark plug look like?

A perfectly fine spark plug will have a greyish-tan color on the electrodes. And the entire body will look like a clean metal.

 Can you clean a spark plug with gasoline?

Yes, you can clean them with gasoline. However, you should not keep the gasoline for more than five minutes per spark plug.

 Should spark plugs be wet or dry?

Dry. If your spark plugs are wet, then that is caused by engine flooding. You can dry the spark plugs yourself or wait till they dry themselves up.


Is it too hard to visually realize your spark plugs have gone bad? We guess not! It is just a matter of examining them to treat them on time. Lastly, always rely on experts to choose the right type of spark plugs for your vehicle to install.