How do spark plugs affect fuel consumption?

In times of constantly changing fuel prices, every driver looks for ways to optimize their costs. We often focus on driving style, tire pressure, or fuel quality, but we neglect a small yet important component hidden in the engine – the spark plugs. Their condition has a direct connection to the vehicle’s efficiency and, of course, how often you visit the petrol station.

Many drivers do not suspect that this relatively inexpensive consumable can be responsible for increasing consumption by up to 30%. Let’s look at exactly how this happens and why you should not postpone replacing them.

The role of the spark in the combustion process

To understand the link with consumption, we need to know how they work. The internal combustion engine operates on a simple principle: it mixes air and fuel, then ignites them. This is where the spark plugs come in. They generate an electrical spark that ignites this mixture in the combustion chamber.

When the plugs are new and in good condition, they deliver a strong and precise spark at the right moment. This leads to complete combustion of the fuel, which means maximum power and efficiency. Every drop of fuel is converted into energy for motion.

How do worn spark plugs increase fuel consumption?

Over time the plug electrodes wear and the gap between them increases. Additionally, carbon deposits and build-up accumulate on them. Here is how this negatively affects performance:

Incomplete combustion (Misfire)

When a plug is old, the spark may be weak or may not appear at all in some cycles. This leads to what is called a "misfire" of the cylinder. Fuel enters the chamber but does not burn completely. It is expelled through the exhaust without having done any useful work. You are literally throwing money out the exhaust.

Loss of power

When combustion is not efficient, the engine loses power. To compensate for this loss and maintain the desired speed, you instinctively press the accelerator pedal harder. The car’s computer supplies more fuel, which again does not burn efficiently because of the poor spark plugs. A vicious circle develops.

Stress on the lambda sensor and the catalytic converter

Unburned fuel can damage expensive components of the exhaust system, leading to incorrect sensor readings and further enrichment of the fuel mixture by the computer.

Symptoms that it’s time to replace them

Besides increased fuel consumption, there are other signs that your spark plugs need replacing:

• hard starting – if the car is hard to start, especially in the morning or in cold weather, the spark is likely not strong enough;
• uneven idling – if you feel vibrations or the engine "stumbles" while waiting at a traffic light;
• sluggish acceleration – the car responds slowly when you press the accelerator.

When should we replace them?

Manufacturers give different recommendations depending on the type of plugs. Our specialists from the OnDrive auto service advise that standard copper/nickel plugs are usually replaced at about 30,000 km. More modern iridium or platinum spark plugs can last up to 100,000 km.

The investment in a set of quality spark plugs is minimal compared to the money you will save on fuel. Regular maintenance restores the engine’s factory flexibility, reduces harmful emissions and, most importantly – protects your budget. Don’t wait for the car to stop starting, have it checked today.