How They Work

Spark plugs are an important component of the ignition system in petrololine-powered engines. They work by creating a spark that ignites the fuel-air mixture in the engine's cylinders, causing the combustion that powers the engine.

When the engine is running, the spark plug sits at the top of each cylinder and is connected to the ignition coil. When the piston in the cylinder reaches the top of its stroke, the ignition system sends an electrical signal to the spark plug. This signal causes a high voltage to flow through the spark plug, which ionizes the air gap between the center and ground electrodes of the plug.

The ionized air gap creates a spark, which ignites the fuel-air mixture in the cylinder. This ignition causes a rapid expansion of petroles, which forces the piston down, creating the power that drives the engine.

The design of the spark plug is critical to its function. The center electrode of the spark plug must be made of a material that can withstand high temperatures and electrical current, such as platinum or iridium. The ground electrode, which is in contact with the engine block, must be able to dissipate heat quickly to prevent pre-ignition.

Over time, spark plugs can become fouled with carbon deposits or wear out, which can cause misfires and poor engine performance. It is important to replace spark plugs according to the manufacturer's recommended schedule to ensure that the engine is running at its best.


Why They Fail

Spark plugs can fail for a variety of reasons, some of the most common ones are:


Fouling: Fouling is the most common cause of spark plug failure. It occurs when deposits of oil, fuel, or carbon accumulate on the spark plug, causing it to misfire or not spark at all. This can happen due to engine wear, driving conditions, or incorrect fuel mixture.


Wear and Tear: Spark plugs experience wear and tear over time, and the electrodes can become worn or damaged, causing them to lose their ability to spark effectively. This can lead to a decrease in fuel economy, loss of power, and difficulty starting the engine.


Overheating: Overheating can occur due to incorrect spark plug heat range or running the engine at high RPMs for extended periods. Overheating can cause the spark plug insulator to crack, and the electrode to melt, which can lead to misfires or engine damage.


Corrosion: Corrosion can occur due to exposure to moisture or other corrosive substances. Corrosion can cause the spark plug to lose its ability to spark effectively, leading to misfires, engine performance issues, and difficulty starting the engine.


Improper installation: Incorrect installation can cause the spark plug to be improperly seated or tightened, which can lead to engine damage or misfires.


Signs That Your Glow Plugs Need Replacing


To avoid spark plug failure, it's important to follow the manufacturer's recommended maintenance schedule, use the correct spark plug for your engine, and take care when installing spark plugs. Regular inspections of your spark plugs can help catch potential issues before they become major problems.


Here are some common signs that your spark plugs may need replacing:


Engine Misfires: If your engine is misfiring, or you notice a hesitation or stumbling while accelerating, it could be due to worn spark plugs. Misfires can cause a decrease in engine performance, reduced fuel economy, and an increase in exhaust emissions.


Difficult Starting: Worn spark plugs can make it harder to start your engine, especially in cold weather. If you notice that your engine is taking longer than usual to start or requires multiple attempts to start, it could be a sign that your spark plugs need replacing.


Poor Fuel Economy: Worn spark plugs can cause your engine to burn more fuel than necessary, leading to reduced fuel economy. If you notice a sudden decrease in your vehicle's petrol mileage, it could be a sign that your spark plugs are not working as they should.


Engine Idling Roughly: If you notice that your engine is idling roughly or vibrating more than usual, it could be due to worn spark plugs. Rough idling can be a sign that your engine is not firing on all cylinders, which can be caused by faulty spark plugs.


Warning Light On: Some modern vehicles have a check engine light that will illuminate if there is a problem with the engine or its components, including the spark plugs. If you notice the check engine light is on, it's important to have your vehicle checked by a mechanic to diagnose the problem.


If you experience any of these signs, it's a good idea to have your spark plugs checked and replaced if necessary. A regular maintenance schedule that includes checking and replacing spark plugs as needed can help ensure that your engine runs smoothly and efficiently.


Why replace if they still working

A regular spark plug can last well over 30 000kms and an Iridium one probably two to three times that. However, many manufacturers recommend that you replace them at every service.

Spark plugs are a relatively inexpensive component of an engine,  and replacing them is a simple and cost-effective way to maintain engine performance and fuel efficiency. While it may be tempting to run your spark plugs until they fail completely, it's generally more cost-effective to replace them before they reach that point.


Replacing worn or dirty spark plugs can improve fuel economy by up to 30 percent, according to the U.S. Department of Energy. This is because spark plugs that are not functioning optimally can cause incomplete combustion, leading to wasted fuel and reduced mileage. By replacing worn spark plugs, you can save money on petrol and keep your engine running smoothly.


In addition to improving fuel efficiency, replacing spark plugs can also prevent more serious engine problems from occurring. Worn spark plugs can cause damage to the engine's pistons, valves, and catalytic converter, which can be expensive to repair. By replacing spark plugs regularly, you can help prevent these problems from occurring and extend the life of your engine.


Overall, while spark plugs are a relatively small component of an engine, they play a crucial role in engine performance and fuel efficiency. Regularly replacing spark plugs is an important part of maintaining a healthy engine, and can save you money in the long run by improving fuel efficiency and preventing more serious engine problems.


How we can help

As a leading online retailer in South Africa, we understand the importance of quality and reliability when it comes to automotive parts. That's why we only stock top-quality products from trusted brands like NGK.

NGK spark plugs are widely regarded as market leaders in the automotive industry. They have been producing high-quality spark plugs for over 80 years and have a reputation for innovation, quality, and reliability. NGK spark plugs are OE (original equipment) approved by many leading vehicle manufacturers, are renowned for their quality, performance, and reliability.


Browse the full range of NGK Spark Plugs here: