Spark Plug Basics: Your Questions Answered

Your engine relies on spark plugs every day—which means you do, too. So it's about time we get familiar with these key maintenance parts. You might be wondering how often you need to change your spark plugs, what sort of spark plugs you should use, or whether you need to upgrade your spark-plug wires or other ignition components. Fortunately, these questions are easy to answer. Read on to learn about spark plugs.

Spark Plugs

What do spark plugs do?

Unless you’re driving an electric car, in which case this article definitely isn’t for you, you’ve got what’s known as an ICE or “internal combustion engine.” Now, combustion requires a spark. Spark plugs are a crucial part of your engine because they’re what makes that combustion happen, both at ignition and while the engine moves through each combustion cycle during operation. When the plugs aren’t doing their job, your engine’s not getting the full combustion benefit. Everything from acceleration and fuel economy to engine smoothness is going to be negatively affected.

How do I know when to replace spark plugs?

Your spark plugs should be changed at the interval given in your owner's manual, typically every 30,000 miles. If no interval is given, or if you recently bought the car and aren't sure when the spark plugs were last replaced, or if your car is showing symptoms of failing spark plugs or ignition issues (trouble starting, misfires, or rough idle), you'll want to replace them. Replace them every 20,000 to 40,000 miles in the future, depending on your vehicle type and your use case.

If you have a high-performance sports car that regularly sees high revs, you will want to change your spark plugs more often. If you drive at moderate speeds and under moderate acceleration, your plugs may last 40,000 miles or more while still operating efficiently. Because spark plugs are cheap, however, and easy to replace, it's good insurance to change them sooner than later, no matter what vehicle you own or how you use it.

How can I check to see if the spark plugs need replacing?

As a general rule of thumb, if something seems funny about your engine, you should check the spark plugs first. If you’re a hands-off kind of car owner, of course, you’ll just take it to your mechanic and get it diagnosed. But if you want to inspect the plugs yourself, it’s a pretty easy job.

Check your owner’s manual to find out where the plugs are located, and then pop the hood and have a look. If the plugs appear dirty, that could mean you’ve got an oil leak or excessive carbon deposits. And if they look damaged, your engine might be running too hot or misfiring.

Keep in mind, though, that even if your spark plugs look fine, they might be past their prime. Consult your owner’s manual for when to replace spark plugs. If you think you’re past due, we recommend replacing them, just to be safe.

Can I replace my own spark plugs?

Although you can check them, you may want to have someone else replace them. Truth is, for a seasoned backyard mechanic, popping the old plugs out and putting new ones in is pretty straightforward. But if you haven’t done it before, you should probably have someone looking over your shoulder the first time through.

There’s some serious wrenching going on here—literally. You'll need a number of tools to complete the job. You need a socket wrench, and you may need a specific spark-plug socket and other accessories as well. Plus, there’s a fairly advanced technique called “gapping” that may or may not be required, depending on your vehicle’s age and other factors.

Wait for the engine to cool off first before attempting any replacement. We're talking four hours, minimum. Those plugs are responsible for combustion, remember? Better safe than scalded.

What spark plugs do I need?

As for which type of spark plugs you'll need, most folks will want to stick with the plugs recommended in their owner's manual. For more info, here's a ton of detail on the different types of spark plugs.

What about cleaning spark plugs?

You’ll find various home remedies for cleaning spark plugs, but for peace of mind, we recommend just swapping them out if they’re that dirty. But it's your call on that front. From a money perspective, spark plugs are a car owner’s dream, because they’re an essential engine part that’s also inexpensive.

Do I need to change the spark plug wires?

Short answer: Yep. Find out how to troubleshoot spark plug wire problems and check out how to replace spark plug wires.

Do you change your own spark plugs and wires? Share your tips and tricks. Leave us a comment.

Last updated June 6, 2017

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