Spark Plugs 101

Advance Auto PartsA lot of people come to me for car advice, and here’s one thing I’ve noticed: everyone thinks they know about spark plugs, but almost no one really does. So I decided to make this column all about spark plugs, because trust me, your engine relies on them every day–which means you do, too. That’s why I want you to get familiar with these little buggers. Let’s dive right in with a little Q&A.

What do spark plugs do?

Here’s a fun fact about your engine: 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, which stands for “internal combustion engine.” Now, combustion requires a spark, doesn’t it. See where I’m going with this? 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, so everything from acceleration and fuel economy to engine smoothness is going to be negatively affected.

How do I know when to replace spark plugs?

My rule of thumb is that 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 they look fine, they might be past their prime. Consult your owner’s manual for when to replace spark plugs, too, and if you think you’re past due, I’d recommend replacing them, just to be safe.

Can I replace my own spark plugs?

Now, I said you could check them, but I didn’t say you should try to 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 like me looking over your shoulder the first time through. I know the internet’s full of DIY guides on how to change spark plugs, but there’s some serious wrenching going on here–literally. 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.

Promise me this: if you do try one of those tutorials on how to change spark plugs, please, wait for the engine to cool off first. I’m talking four hours, minimum. Those plugs are responsible for combustion, remember? Better safe than scalded!

What about cleaning spark plugs?

Here’s where I differ from a lot of DIY-ers. You’ll find various folk remedies for cleaning spark plugs, but for peace of mind, I say just swap ’em out if they’re that dirty. Because how much money are you really saving, right? Twenty bucks? Fifty? Spark plugs are a car owner’s dream, really, because they’re that rare important engine part that’s also inexpensive. If it’s my car, I believe my engine’s worth that kind of investment, every day of the week. Give it the shiny new plugs it deserves.

What do you think?

I’ve seen a few spark plugs in my day, but I’ll be the first to admit, this article isn’t the last word on the subject. Got anything to contribute? See things differently? Chime in with a comment, and help me and everyone else here understand where you’re coming from.


Editor’s note: For more info on these DIY essentials, check out the Resources & Video section at Advance Auto Parts.


  1. If you can check your plugs yourself, you can replace them yourself. Removing & replacing them are the difficult aspects. If you are going to go so far as to learn hw to achieve that (and actually remove them) you are certainly capable of gapping and installing a new set.

  2. I find no real fault with your article except the fact that you felt the need to inform the readers that they have (what’s known as an ICE, which stands for “internal combustion motor.”) Wouldn’t ICE stand for “Internal Combustion Engine”?

  3. ICE – Internal Combustion Engine

  4. From my personal experience, I have found that the best choice for spark plugs is original equipment. Other spark plugs from other manufacturers may work fine, but for top performance I prefer O.E. If it’s a GM product, I use AC. If it’s a Ford product, I use Autolite. Champion seems to work well in Chrysler products, but I haven’t had the greatest success with them in a GM product.

    • Sorry John, I disagree. For Fords Motorcraft plugs are much better. I’ve used both. Autolites come pregapped but don’t last as long.

    • David Ondre says:

      My Chevy’s run great with Autolites. (My Elantra does too ;-). Ford had the name years ago but Allied Signal &/or Honeywell owns the name now.

    • I never had luck with Champion plugs in high mileage Chrysler LA engines. Switching to Autolite solved a lot of my plug fouling problems.

  5. You forgot about diesel engines! They too are “ICE” and don’t utilize spark plugs.

  6. Pat Hennigan says:

    I’m a novice when it comes to spark plugs. The blog posting said that the necessity of gapping might depend on the age of the car. I’ve got a 2010 Honda Civic with 49000 miles. Is gapping needed and what are the recommended plugs for that model?

  7. Should you remove the spark plug with the engine dead cold, warm, hot or what,
    I heard that removing them hot may strip the threads in the head, Loosen them a bit and turn them back in to looses carbon build up inside the head, rather than dragging that carbon through the threads , blow out the recess around the plug before you remove it completely to avoid getting that dirt inside the cylinder use a piece of vacuum line on the end to aid in putting the plug back in, less chance of cross threading or stripping the threads with the wrench and the line is flexible for getting into hard to reach places I could go on and on. Well I guess I HAVE

  8. On older cars an easy test was to try to run up to 80 in passing gear. If the engine started stuttering instead of upshifting, it needed new plugs. Now I have an 11 year old Buick with original plugs and 55000 miles and no problem, except this: reaching the rear bank of plugs appears impossible without disassembling some of the many things between the back side of the engine and the close firewall.
    I am guessing that replacing the plugs at the recommended 100,000 miles will require considerable labor cost in addition to the expensive plugs. It will be the second time in my long life I let anyone else change my spark plugs. The first time the mechanic installed the wrong plugs and wrong new rotor, the wrong rotor resulting in breakdown out in the sticks on Sunday afternoon.

    • jack the car up and use jack stands to allow the wheels to drop. you may have to remove the wheels. and you can on many older cars gain access to the plugs through the fender well. especially older full size GM’s

  9. Blake Davis says:

    Why write an article about sparkplugs without talking about heat ranges?

  10. The article is lacking unless you are targeting people who have no experience with automotive maintenance. If you are to explain when to replace spark plugs that are “dirty” then you need images that depict good, bad, or dirty. You need to test your article on your target audience before publishing it. Feel free to contact me if you have any questions.

  11. Forget gapping, just buy E3.

  12. Tom Fetchko says:

    Don’t forget to use dielectric grease on the boot connections on the plugs and the coil connections. It water proofs and helps to prevent miss firings.
    Some Ford vehicals do not have plug wires. The have a ignition coil mounted on top of the spark plug.

  13. Austin Dollar says:

    Just a couple of things to consider for additional discussion.. Special tools (magnetic spark plug socket), plug wire pullers, proper plug selection (OEM) or resistor vs non-resistor, proper torqueing, using anti-seize and dielectric grease, and maybe advanced discussion such as reading plugs, heat ranges, and the little known art of indexing plugs..

  14. was told to change spark plugs and wires together.
    relatively easy to recognize worn plugs.
    if wires are not frayed,cracked,etc., how to determine
    if they should be replaced?

  15. One little factoid you left out was the fact that the electrodes wear away with use. This really can’t be undone. The newer coatings like platinum and iridium slow this down, but don’t stop it. That’s why we have such long change intervals now. I also think 100k mile intervals are b.s. That’s just automakers advertising low-maintenance cars. Even the best plugs are getting tired at 30-40k miles. It’s a false economy to try and stretch these cheap parts out to 100k.

    • Sorry, have to disagree. Platinum and especially iridium spark plugs hold up remarkably well. I got 200k miles on the original platinum plugs on a 2005 Hyundai SantaFe with no reduction in gas mileage nor performance. I changed the platinum plugs on my 1990 Toyota Supra at 100k just because it hit that mark. Again there was no difference in gas mileage nor performance. I wouldn’t recommend most people attempt this, rather they should stick to the manufacturer recommendations. (Note: 95% of my driving is highway miles).

      As a mechanical engineer that does almost all of our vehicle maintenance, I’ve been delighted at not changing spark plug as frequently as I did years ago. Especially given how difficult it is to get to the plugs in some engines.

  16. Bills garage says:

    I don’t know about you people, but, when the article starts off defining an ICE as “an internal combustion motor”, I start thinking.

    First of all a “motor” has no combustible parts. A motor is an electrically driven device that provides power without the use of any type of combustible fuel.

    An internal combustion engine provides power by using a fuel that is combustible to produce power.

    To define an ICE as a combustible motor that lives in your car is total nonsense. The guy sounds like an idiot to me, an if that’s how his article starts, I’m Leary of the follow up info because he is blatantly wrong from the start.

    Unless you have a totally electric car, the only motors in your car control the fan, the power seats and windows, and windshield wipers.

    ICE stands for “internal combustion motor”. What an idiot. ICE stands for Internal Combustion Engine.

    Car Motors do not move cars forward if they have an ICE.

  17. Bills garage says:


    Car motors do not move cars forward. Most cars move forward because they have an ICE. Combustible fuel engine vehicles, DO NOT have a MOTOR, of any horsepower, under the hood. It is called an engine; for a reason.

  18. Robert Chambers says:

    The thing that makes the car go is an ENGINE, not a motor (unless you are driving an electric automobile) most ENGINES use a starter MOTOR to crank them over for inital start up. If you are giving advice about things call them by thier correct nomenclature.

  19. Just buy Bosch Platinum +4’s and don’t worry about it for 30K miles. Never have to gap and they are very reliable and give top performance. To hell with OEM!

  20. David Ondre says:

    Also, as specified above, seasoned backyard mechanics have a hard time changing plugs on transverse V-6 engine cars. And some rwd cars (i.e. LT-1 Camaro/Firebird from the 90’s) are day long headaches to get to the plugs.

  21. Always recheck the Gap… Don’t trust the Manufacture to be gaped right..

  22. Another Bill says:

    I’ve done routine maintenance on my vehicles all my life. I currently have a 2005 Nissan Frontier V6 and a 2005 Honda CRV 4-cyl. I want to change the plugs but the idea makes me wonder. They are difficult to even access, with stuff to remove that I’ve never before encountered. Any ideas to make the job easier?

  23. DEFINES A motor AS a comparatively small and powerful engine, especially an internal-combustion engine in an automobile, motorboat, or the like. So I think he NAILED it

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