What Do Spark Plugs Do?

After a long, exhausting day at work, all you want is to get home. You toss your things in the backseat of your car, sink into the driver’s seat, and turn the key, eager to leave the day behind. But instead of the reassuring hum of a healthy engine, you're met with sputtering, knocking and an unsettling silence. You try again—same result.

Frustrated, you glance around for help, just as a co-worker walks past. Thinking it might be a dead battery; you flag them down for a jump. They oblige, but your vehicle refuses to cooperate. Something is missing—something crucial to bring your engine to life. There is just no spark.

So..what do spark plugs do?

If your vehicle’s gas-powered engine isn’t starting smoothly, then a faulty or fouled spark plug could be to blame. 

A spark plug is a small but essential component that ignites the fuel-air mixture in your engine’s cylinders. This controlled explosion powers the pistons and crankshaft, converting stored energy into motion. Without it, your engine will be unresponsive—lifeless when you turn the key or push the ignition button.

The internal combustion engine process

When you attempt to start your vehicle, electricity from the battery travels to your vehicle’s induction coils where the initial 12 volts are amplified to up to 45,000+ volts. The increased voltage is then transferred to the spark plugs where the electricity jumps, or arcs, across a gap between two leads. This arc is what ignites the air/fuel mixture to create the explosion that your internal combustion engine depends on to operate. 

Spark plugs are made to be durable, capable of enduring countless ignitions before breaking down. However, they do deteriorate over time. This breakdown could lead to misfiring, rough idling and even a total failure to start.

How to know your spark plugs need to be changed

Your vehicle’s refusal to start is only one potential sign that your spark plugs are failing. It is possible to drive your vehicle with bad spark plugs, but if you do, you will experience signs of deterioration. So how do you know that your spark plugs are the root of the problem? Here are a few symptoms to watch out for.

• Poor fuel efficiency – While fuel efficiency can decline for various reasons, misfiring spark plugs can waste fuel and reduce mileage. If you notice a decrease in fuel efficiency, it may be wise to take your vehicle in to determine if there is a deeper issue.
• Poor performance – A bad spark plug could result in sluggish or inconsistent power when accelerating. Hesitation when you attempt to accelerate quickly could be an indicator that your plugs are misfiring. When stopped, you may also experience rough idling, vibrations or your vehicle may even stall.
• Hard start or non-start – If your vehicle starts with jerky, rough movements or makes knocking noises but won’t fully start, your spark plugs may be deteriorating.
• Knocking or rattling noises – If your plugs are misfiring there will be a constant pinging sound emanating from your vehicle. These sounds originate from your engine.

If you notice any of these symptoms, then it may be time to change your plugs or have a professional inspect your engine to find out exactly what is happening.

How often should spark plugs be changed?

Most manufacturers recommend changing spark plugs every 30,000 to 100,000 miles to prevent performance issues. However, factors like spark plug type, engine design and overall engine condition may require replacement sooner. Always refer to your owner's manual and maintenance schedule for your vehicle. Regularly replacing spark plugs ensures smoother starts, optimal combustion and improved fuel efficiency.

Your vehicle depends on one of three different types of spark plugs to get you from point A to B: Iridium, Platinum, Copper.

• Iridium - These are the highest quality, and longest lasting spark plugs on the market. Their fine wire center electrode conducts electricity better than the other two options.
• Platinum – These plugs have a higher melting point that allows them to withstand higher temperatures. This allows them to last up to 100,000 miles. They depend on a platinum disc that is fused to the electrode to conduct electricity.
• Copper – These plugs are the most common but deteriorate the fastest. They last roughly 20,000 miles and conduct electricity through the copper core and nickel alloy that is fused to the electrodes.

The time it takes to change your plugs varies by vehicle make and model. Some vehicles are straightforward while others require components to be removed for service technicians to reach the plugs. Additionally, your vehicle must be cold for the plugs to be changed so plan to leave it at the shop for a while before it can be worked on.

Electric vehicles and spark plugs

Unlike gas-powered vehicles, electric vehicles (EVs) don’t require spark plugs. That’s because EVs don’t rely on internal combustion engines to generate power. Instead, they use battery packs and electric motors, which deliver instant torque without the need for fuel-air ignition. This fundamental difference means EV owners never have to worry about spark plug replacements, misfires or ignition failures—just another advantage of going electric.

Keeping your vehicle in peak condition is all about staying ahead of potential problems. Spark plugs may be small, but they play a big role in keeping your engine running smoothly. By recognizing the signs of wear and knowing when to replace them, you can avoid poor performance, wasted fuel and unexpected breakdowns. Regular maintenance ensures that when you turn the key or press the ignition button, your engine responds without hesitation.

The next time your car hesitates to start or your fuel efficiency drops, don’t overlook your spark plugs. A little preventive care can go a long way in keeping your engine healthy and your daily commute hassle-free. Whether you’re replacing them yourself or trusting a mechanic, staying proactive with maintenance will save you time, money and frustration down the road.