What Do Spark Plugs Do And How Often Do You Need To Have Them Replaced?

While drivers know that they need to have the oil in their cars changed regularly, many neglect their spark plugs. Spark plugs are simple, inexpensive components that perform a big role in your car's engine — they're responsible for the actual ignition process that transforms gasoline into the energy that your car needs to move. They wear out over time and need to be replaced on schedule in order to avoid poor engine performance and decreased gas mileage. To learn more about the spark plugs in your car and how often you need to have them replaced, read on.

What Do Spark Plugs Do?

Your car's engine has a spark plug for each one of its cylinders. The metal portion of the spark plug sits inside the cylinder's combustion chamber, which has a mixture of air and gasoline injected into it.

When your car's ignition system determines that it's time for the spark plug to fire, it sends a high-voltage current through the ignition coil and into the spark plug.

The electric current travels through the spark plug to its central electrode, where it arcs between the central electrode and the L-shaped electrode below it. This ignites the fuel-air mixture in the combustion chamber and pushes the piston in the cylinder downwards.

The movement of the piston turns your car's crankshaft, which provides its ability to accelerate. In essence, your spark plugs are the components that turn your car's fuel into the energy it needs to move.

Why Do Spark Plugs Fail?

The most common reason that spark plugs begin to fail is due to age. Combustion causes carbon to build up on the electrodes, which increases their electrical resistance. Additionally, corrosion can cause the metal electrodes to become dull. Both will cause the worn-out spark plugs to fire later than your car's engine system wants them to, which causes engine misfires.

Spark plugs can also become fouled by your engine's oil. Oil builds up on the surface of the electrodes, acting as an insulator and preventing them from firing at all. This happens most often to drivers who only make short commutes in the city — when the engine never gets hot enough to burn the oil off of the spark plug's electrodes, they eventually become covered in oil.

How Often Do You Need to Replace Spark Plugs?

You'll need to replace your spark plugs according to the maintenance schedule in your owner's manual. Copper spark plugs typically need to be replaced every 30,000 miles, whereas long-life platinum or iridium spark plugs can last for up to 100,000 miles before they wear out.

It's possible for your spark plugs to wear out prematurely if you do quite a bit of highway driving — more engine RPMs place greater wear on your spark plugs. You can tell that they're wearing out when your engine starts misfiring. You'll have uneven performance when you accelerate, and your check engine light may flash momentarily.

If your spark plugs have been fouled by oil, you'll need to have them replaced regardless of your car's maintenance schedule. When you frequently have trouble starting your car and the engine runs poorly until you've driven around for a while, your spark plugs may be coated in oil and need replacement.

Your car's ignition system is designed for either copper spark plugs or long-life spark plugs, so it's not recommended to switch the type you're using. You'll also need to have all of them replaced at the same time.

Whether your spark plugs are worn out or coated in oil, take your car to an automotive repair shop to have your spark plugs replaced. Spark plugs are inexpensive, and a skilled mechanic can replace them quickly. DIY guides to replace spark plugs exist, but there's always a risk that you may break an ignition coil or damage your ignition system while you're attempting to replace them — it's safer to have it done at an automotive repair shop.

To learn more, contact an auto repair shop.