What Can Happen if You Use the Wrong Spark Plugs?

When you’re out and about driving, the last thing you want is for your spark plugs to fail. Spark plugs are one of the many components that keep your car running efficiently, so they must be replaced whenever they wear out. Most spark plugs will last at least 30,000-40,000 miles.

Just remember you’ll need to buy spark plugs suitable for your car’s engine. It might be hard for the untrained eye to spot the differences between each set, but not all spark plugs are universal. Using the wrong set could affect your vehicle’s performance and, in extreme cases, potentially cause an accident.

Does a car really need plugs?

Two people looking under the hood, potentially at the wrong spark plugs.
Two people looking under the hood | Getty Images

Spark plugs are connected to threads that plug into your car’s engine, either on the side or top of the engine block. Turning your key in the ignition switch or using push-button start activates your car’s starter. From there, the energy produced by your car’s battery travels to the spark plugs. 

The plugs are responsible for igniting the air/fuel mixture and converting it into kinetic energy. Once that’s done, your engine will run seamlessly until you reach your destination. If just one spark plug is missing, it will cause your engine to produce a lot of noise and likely sustain severe damage.

Don’t use the wrong spark plugs for your car

When it’s time to replace your spark plugs, Jalopytalk cautions readers that specific engines need specific spark plugs. While your replacements don’t have to match the old OEM ones, they should at least be the same type. Iridium spark plugs offer great performance, but they shouldn’t be used with engines that usually utilize copper or silver spark plugs.

Many auto part suppliers offer an online registry where you can find the right spark plugs that fit your vehicle. If your owner’s manual has the part number, you may not even have to provide any additional information. Even if the owner’s manual doesn’t list replacement spark plugs, it’s still possible to locate them with your car’s other details. 

You’ll have to provide the model and make of your car, as well as its model year. Additional information, like the engine displacement or the number of cylinders, might also be required. Once you’ve got the parts, you can either install them on your own or have a mechanic do it for you.

In most cases, it’s very easy to determine if you’ve purchased the wrong spark plugs. If the plugs aren’t the right size, they won’t even fit inside the threads. Also, before you install the spark plugs, check to make sure that there’s no damage to the electrode.

Here’s what might happen if you use the wrong spark plugs

Even if you manage to fit the wrong spark plugs into the threads, they likely won’t stay attached for very long. Driving with missing or bad spark plugs will likely cause a lot of hard starts and rough idling. When your spark plugs aren’t firing at the correct times, an instance commonly known as an engine misfire, you’ll hear a distinct rattling sound.

When your spark plugs aren’t firing properly, it can also hamper your vehicle’s acceleration and lower its fuel economy. Incomplete combustion can also occur when the spark plugs can’t fully ignite the engine’s air/fuel mixture. This will probably cause your engine to start smoking.

Eventually, your car may lose power and refuse to start at all. That’s why it’s important to never ignore the warning signs of bad spark plugs. Spark plugs are relatively inexpensive to replace: your engine isn’t.

RELATED: How to Safely Change Your Spark Plugs and Ignition Coils