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What Does a Bad Spark Plug Look Like 2023 [Updated]

A bad spark plug looks like a worn-out part, right? Well, it turns out that sparks from a bad spark plug can cause serious damage to your vehicle and even leave you stranded miles away from home or work.

When things go wrong inside your car, you don’t want to spend hours searching for a mechanic. That’s why it’s important to know the symptoms of a faulty spark plug before you get stranded somewhere far from home.

It’s important to note that a bad spark plug won’t necessarily produce a loud pop or smoke. If you suspect broken spark plugs, check them using these key signs.

Then call your local repair shop to have them replaced with new spark plugs as soon as possible.

Indicators of bad spark plugs

Here are some prominent indicators of bad spark plugs:

Spark Plug Gap

Although the spark plug gap could be a hundredth of an inch and not detectable by the naked eye, it could be a possible reason for spark plug failure. We recommend using a spark plug gap tool to adjust the gap as needed. Refer to the manufacturer’s manual to know the exact positions of the spark plug.

Sporadic Engine Rumbling

A rumbling sound coming from the engine compartment is an indication that something isn’t working properly with the ignition system. The most common reason for this is that one or more spark plugs are faulty.

The noise should come sporadically since it depends on which plug you use. You might not hear anything if the problem is intermittent.

Clicking Noise When Starting Up

It could mean that there is no spark at all. It also indicates that the wires connecting your battery to the spark plugs are loose. Sometimes, a loose wire will make a clicking noise when turning over the engine.

To fix this issue, tighten the bolts holding the connectors together. Then reconnect the ground wire and test again.


Any problem with the air-fuel mixture combustion causes a misfire as the mixture ignites early or not at all in the cylinder. Unburnt fuel leads to harmful exhaust emissions. Engine misfire results from the bad spark plug, producing a sputtering sound and leading to the loss of power.

You may also experience violent shaking. Constant engine misfires lead to vehicles poor performance.

How Does A Bad Spark Plug Look Like?

Here are some of the cases which helps in identifying bad spark plug look:

Cracks in the Shell

Usually, cracks form in the shell after the spark plug has experienced long periods of stress. Cracks occur mostly around the base of the metal cylinder head cover where the spark plug is located.

If the crack is small, you can try repairing it yourself. Just use pliers to remove the broken piece of metal. However, if the crack is deep enough, you should take it to a professional mechanic so they can clean it out and restore the surface.

If you see cracks above the spark plug hole, this is another sign that it needs replacing. If that happens, then take it to your local service centre.

Carbon Deposits

The deposition of torsion toward the middle or end of the spark plug may hinder its proper working. You can observe in its conductive terminals – a black and sry mark. It could be due to using the wrong spark plug or driving slower than normal.

For a long time, the oil deposits on the spark plug.

Any spark plug error is attributed to the long term retention of oil on it. The electrode tip has oil, and there is a black deposit on the body of the spark plug. It is important to locate the source of oil leakage as it may be leaking into cylinders. Take the help of a mechanic to resolve the problem of leakage. Once sorted, you can replace the spark plug.

A wet spark plug

If you notice certain drops of water on the spark plug while inspection, it means that the plug is soaking into water. If you often drive your vehicle in the rain, there are possible chances of water seeping into the engine and damaging the spark plug. When the spark plug is soaked for so long, it may lead to rising and corrosion.

on fire

Spark plugs undergo a lot of heat for igniting fuel. Hence, the failure of the spark plug may lead to a fire. Once you disassemble the spark plug for testing, you can feel the heat. Improper installation or the spark plug inside the engine could be too loose are the two prime reasons for fires.

Rusted Plugs

If your spark plugs look rusty, they probably aren’t functioning correctly. Check the terminals for corrosion and replace them if necessary.

Frequently Asked Questions

Is it bad to drive with faulty spark plugs?

Yes, never drive your vehicle when spark plugs wear out as they may cause irreparable damage to the internal combustion engine. Replace them with the correct spark plug before starting the engine.

How can you tell a bad spark plug?

Some of the primary symptoms indicating fouled spark plugs are engine surging, slower acceleration, rough car start, and poor fuel economy.

What colour is a bad spark plug?

You can find tan tint or slightly brown towards the ground and centre of electrodes as a spark plug in a healthy engine. If you find the carbon or oil deposition, it indicates the faulty spark plug.


The sparks which come from the spark plug play a major role in the combustion reaction process. To ensure the efficiency of the internal combustion engine, the spark plugs are required to work perfectly. Any malfunctioning or faulty condition of the spark plug will affect the engine’s overall performance. Therefore, it becomes necessary to check the spark plugs’ functionality regularly. These tests should be conducted by taking the help of professionals who are well equipped with all the equipment, tools, and expertise needed to carry out the test.

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My Name is Christopher Angels, and I am a postgraduate in mechanical engineering. Cars have always excited me as a child, and soon I decided to dive into the world of cars by pursuing mechanical engineering. I also worked as a Mechanic for over 3 years to understand Cars' anatomy and how each part contributes to its working.

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