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What Does A Bad Spark Plug Look Like – Know Your Engine

What Does A Bad Spark Plug Look Like

What does a bad spark plug look like

You are still wondering how to identify bad spark plugs just by looking at them? Then let us tell you, it is the most straightforward job to do. Even if you know nothing about vehicle parts, these symptoms are pretty easy to understand. Read out further to more!

What Does A Bad Spark Plug Look Like

4 Signs to identify bad spark plugs:

1. The outer part looks burnt

Die to excessive overheating, the spark plugs get burned from the outside—also, some of the internal and external wires burn, which are negligible to the eyes.

2. Insulator looks carbon-fouled

At first glance, you will see the insulator tips look soot-black due to excessive carbon buildup. It is the result of inefficient spark plugs.

Signs To Identify Bad Spark Plugs

3. Electrodes get broken

When you notice the electrodes broke, you know those spark plugs are not for your vehicle. Hence, they couldn’t function to that potential.

4. Worn out exterior

With time, the spark plugs wear out and look rusted from the outside. It means they are about to stop working and need replacement.


Carbon fouled spark plug

carbon fouled spark plug

What do spark plugs tell you about your engine?

So, what can spark plugs tell you about the health of your engine? Here’s the rundown:

  1. A fouled spark plug signals that your car isn’t running at its peak performance. This could indicate that your air filter is dirty or your car’s ignition timing is distorted.
  2. A spark plug that is too hot can cause it to wear out quickly, as the metal and insulation can deteriorate. Too much heat is often due to a misfiring spark, so if your spark plugs are consistently running hot, it’s time to get your car checked out.
  3. A spark plug not providing a spark can indicate that a spark plug wire is disconnected, corroded, or worn out. Checking the health of your car’s spark plug wires is easy; a qualified mechanic can quickly check for your peace of mind.
  4. Dark soot around the spark plug tip is usually caused by an incorrect fuel/air mixture, often due to a clogged air filter. If your engine has a too-rich fuel/air mixture, it emits too much-unburned fuel, leading to sooty deposits and poor performance.
  5. The gap in between the spark plug electrodes is an important factor in engine performance. If the gap is too big or too small, you can experience an unreliable engine and poor performance. It’s easy to check the gap; your mechanic can measure it with a spark plug gap tool.

Do bad spark plugs give a check engine light?

Yes! When spark plugs misfire, they can cause difficulties with your vehicle’s performance, resulting in an illuminated check engine light.

Can bad spark plug damage the engine?

Bad spark plugs can mean poor or inconsistent performance or cause complete engine failure. Poor spark plugs can lead to poor combustion, resulting in motor damage or a misfire. 

Poorly gapped spark plugs can lead to fouled or misfiring spark plugs and can even cause complete engine failure if worn improperly. When spark plugs become too worn or dirty, it decreases the efficiency of the combustion process and reduces engine performance.

What causes spark plugs to be wet with petrol

If your car is running poorly or won’t start, one of the possible culprits could be wet spark plugs. An engine flooding issue typically causes wet spark plugs. The fuel injection system has introduced too much fuel into the engine, resulting in much fuel entering the cylindrical chambers around the spark plugs and dampening them.

How to read spark plugs for rich or lean

The main way to read spark plugs for rich or lean is to look at their color. Ideally, your spark plugs should be brown and dry, indicating a well-balanced and healthy engine. If your spark plugs have black soot or are wet, this indicates that your engine is running too rich – as a result, fuel is being wasted, and pollutants are being created. 

How does a car run with a bad spark plug?

While an engine can run with a bad spark plug, it will not run or operate at its optimal level. This might cause difficult starts, misfires, rough idle, poor acceleration, and poor fuel efficiency. In the worst case, a faulty spark plug can cause serious damage to the engine. 

What do bad spark plugs sound like?

Bad spark plugs often create a rhythmic, ticking sound that resembles engine knocking caused by air/fuel mixture ignition in the combustion chamber too early.

What happens if you don’t change spark plugs?

Here’s why you need to stay on top of your spark plug replacement schedule:

1. Poor Engine Performance

Poor engine performance is one of the most noticeable side effects of old spark plugs. Over time, spark plugs will wear out and can no longer ignite the air and fuel mixture effectively. As a result, your engine won’t run as efficiently, leading to decreased power and acceleration.

2. Hard Starts

If your spark plugs are old or become fouled with debris or oil, they may not be able to fire efficiently. This can make it difficult to start your car, or cause it to take an abnormally long time to warm up.

3. Reduced Fuel Economy

When the spark plugs in your car are worn out, the engine computer can no longer adjust the air and fuel mixture for optimal efficiency. This can lead to increased fuel consumption, resulting in higher fuel costs for you.

4. Spark Plug Failure

If old spark plugs are not replaced on time, the electrode can fail, resulting in a spark plug misfire. In some cases, the spark plug can become embedded in the engine cylinder head, causing engine damage that can run up a hefty repair bill.

How do you check spark plugs without removing them?

The first step in checking spark plugs without removing them is to open up your vehicle’s hood and locate the spark plugs. 

Next, look at the cover and threads of the spark plugs. The cover of the spark plug should be clean and not have any cracks or discoloration. 

Finally, if all the visible parts of the spark plug appear in good condition, you can check the spark plug further by checking the gap. 

What Causes A Spark Plug To Turn Black – Oil Deposits

What causes a spark plug to turn black

What does a good burning spark plug look like?

What does a good burning spark plug look like

Frequently Asked Questions

#1. Is it bad to drive with faulty spark plugs?

If you know your vehicle’s spark plug has gone bad, it is better to drive with it anymore unless you change them. The car’s engine will stop working if you continue driving with bad spark plugs.

#2. What happens when one spark plug goes bad?

Some primary symptoms that bad spark plugs give out are slower acceleration, poor fuel economy, rough starting of car and engine surging.

#3. How long does a spark plug last?

An average to good-quality spark plug lasts up to 80k-100k mileage, depending on the type of vehicle. However, this may vary in different manufacturers, and mileage can be high in top-notch models.


Lastly, we want to tell you that if you see any of those symptoms on your spark plug, contact a mechanic and get them replaced if needed. Do keep a maintenance routine for spark plugs to increase their life.

You won’t like rough and unsteady car drives, right? So, get them replaced once and for a long time.

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