What are engine spark plugs & what do they do?

There are thousands of parts that make up your car. They all work together, from small bolts to important components to keep your car running. Spark plugs are common and well-known among car enthusiasts. These parts are situated in the engine block and are responsible for many operations.

Article summary

Spark plugs generate the necessary electricity to start your car. They’re usually effective for up to 100,000 miles. However, when they go bad they’ll exhibit some of the following symptoms:

  • Engine misfiring
  • Rough sounds from the engine
  • A lack of acceleration


The simple task of starting your car is usually effortless. All you have to do is turn the key over. Whether you drive a Mazda RX8 or a Ford F150, this task is similar across all vehicles. But if you experience signs of a bad spark plug, you will not be able to complete the ignition process.

If you are curious and ask yourself what engine spark plugs are and what they do, continue reading as we explain them in detail. 

Table of Contents

What are engine spark plugs?

4 Spark Plugs

Spark plugs are one of the many components that make up the entire car. They are devices used for delivering an electric current to the combustion chamber. This current comes from the ignition system. With the help of spark plugs, it ignites the compressed fuel mixture by generating an electric spark.

The first spark plug was used in 1860 on the first internal combustion piston engine. Since then, this part was continuously upgraded, but the operation has remained the same. 

Composed of a shell, this part has a central conductor and an insulator. It is situated in the engine block and has additional protection against extreme temperatures and high pressures.

What do they do in a car?

The basics of this component are easy to understand. Spark plugs generate electricity that ignites the combustion needed to start your vehicle. These parts are essential for your car because it won’t start without them. Whether you drive a Toyota or a Chevy, the engine will not start with broken spark plugs.

The air and fuel mixture is useless in its raw form. This mixture has to be ignited to put your vehicle in motion, and the spark plugs are responsible for that. They send a bolt of electricity across a small gap in order to make the mixture effective. But when the spark plugs are failing, the electricity will not be strong enough to light up the mixture. 

How long do they last?

Your vehicle’s parts are built from strong materials, and they are designed to last a long time. But they have a finite lifespan, and you will have to replace them over time. The spark plugs are essential to your engine, and your car will not work without them. 

But these components are constantly exposed to the extreme heat of the engine, its vibration, and the high pressure it generates. While they are equipped with special insulations and protectors against harsh conditions, these parts will eventually wear out and break down over time. 

You should expect and approximate the lifespan of these parts to be at least 50,000 miles. However, some high-quality spark plugs made from iridium are effective for up to 100,000 miles. Once they break down, replacing them is necessary. 

Here are some things to look for as you’re buying them:

  • Check the owner’s manual
  • Get iridium spark plugs if that’s what the manual says.
  • Get better ones for improved fuel efficiency
  • Buy them from a trusted seller.

Bad spark plug symptoms

When spark plugs go bad, it is important to change them as soon as possible. Without them, your car will not be able to work properly. There are a couple of symptoms to look for, and when you identify them, you will know something is wrong with the spark plug.

The most common symptom of a bad spark plug is directly impacting the engine. It will sound rough and jittery when it is running idle, and this will cause vibrations that can be felt throughout the vehicle. These vibrations are dangerous for other components that might get damaged from the shock.

Your engine will also misfire often. It happens because the cylinders are not firing correctly. Bad spark plugs will also negatively impact the fuel economy and you might have to refuel more often. Lastly, you will experience a lack of acceleration where the vehicle feels unresponsive as you press the gas pedal.

These symptoms are more than enough to tell you that there is something wrong with the car. Investigate further and consider the spark plugs to be the problem. Seek the help of a skilled mechanic and ask them to diagnose the problem professionally. 

Spark Plugs Autolite 85

Sound of bad spark plugs

When the spark plugs go bad, you will hear a specific sound from the engine. When you try to get the car moving and slowly accelerate the car, you will hear a distinct knocking sound coming from the engine bay.

It is a result of the improper detonation of spark plugs. All the fuel inside the chamber will be ignited, and air vapors will be fired instead of ignition. It is how a bad spark plug causes engine knocking that manifests through vibration and a specific sound. 

A perfect blend of fuel mixture is necessary for turning on the vehicle for the combustion process to unfold. The ignition initiates this combustion, and the spark plugs are responsible for delivering the necessary electrical current for this process.


There comes a time when you should change spark plugs, but it is not recommended to replace them if they are still working. That is why you have to check these parts and inspect them thoroughly. Make sure they are not working properly before you decide to change them. 

Additionally, such an inspection can be done from time to time when you do full maintenance of your vehicle. There are a couple of steps you have to follow to check your spark plugs properly.

Champion Copper Plus RN16YC5

While every motorized vehicle will need fuel, heat, and air to work, not all of them will share the same components. Spark plugs are only found in gasoline engines and are exclusive to a specific range of vehicles. Glow plugs are available for diesel ones, and they both have the same purpose.

Both of these parts represent the ignition source. While this component can have some restrictions, you can start a warm diesel engine without needing glow plugs. This situation is convenient in climates with high temperatures where the intake air is hot. 

A glow plug is similar in construction to spark plugs but comes with a heating element at its tip. This element is built from materials that resist oxidation and high temperatures. 

What happens when they go bad?

Champion 807 L78C spark plugs

When these components go bad, the entire vehicle will suffer. You will struggle to start the engine, and when that happens, you will experience lots of knocking and misfiring. These parts are essential for the combustion process. Without them, this process is delayed and misfires can happen.

Several cylinders won’t produce the power they should, and it will be harder for your engine to meet the driver’s requirements. Because the fuel mixture is not ignited, the fuel economy will decrease, and you might have to refuel often. 

You can also notice problems when you stop at a red light. As the engine is idling, the delayed spark makes it difficult to perform this simple process. Additionally, rough idling will be experienced, especially during cold and wet winter mornings. 

The colder your vehicle is, the harder to start the engine with bad spark plugs. As soon as you replace them, you will notice improved performance and an easier engine start. 

Here are some signs to look out for:

  • Slow acceleration
  • Loss of power
  • Poor fuel economy
  • Engine misfires
  • Difficulty starting the car
Bosh platinum spark plugs

How long do they take to change?

When you want to change these parts, there are some costs involved. Firstly, you have to pay for the part itself. Purchase new ones that have the highest quality even though they might be more expensive. Investing in a strong and durable part will ensure its efficiency for a long time. 

If you don’t know the mechanics, it might be difficult for you to change this part yourself. A skilled mechanic will help you with this task, but you will have to pay additional labor costs. If you still decide to do this change, it should take about an hour for a four-cylinder engine.

In most cases, this is a simple job that anyone can do when they are provided with specific instructions. If you have the time and the willingness to learn, you can save a couple of hundred dollars which would have been used for labor fees.

several spark plugs

Why you can trust us?

We love cars as much as you do. And if it anything happens to it, we all get a little bit anxious. To eliminate that anxiety, we are trying to come up with the articles that will help you out with fighting these problems. All the information regarding engine spark plugs & what do they do has been handpicked by us, including the products. Go ahead and fix that faulty part and vroom vroom!

Factors to consider


Spark plugs come various types. Some are with single electrode that are cheap and easily available. Some have multi electrodes that are comparatively expensive but have more life span as there are multiple electrodes that die one by one.


Type of material that the spark plug is made up of says a lot about it. For example, copper spark plugs have life span of around 30000 kilometers and are suitable for in-line engines. While the platinum spark plugs can last up to 120000 kilometers and give the most efficient fuel combustion. So, choose accordingly.

Heat range

The heat dispersal of different spark plugs varies. If you have a low octane fuel then go with the low heat dispersing spark plugs. If your vehicle operates on high octane fuel then high heat dispersing spark plugs are the best choice.

How much do they cost to replace?

If it is a DIY project then it will cost you cost you around $5-$20. But if you plan to get it changed by a professional it might put a dent of approx. $100-$120.

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