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Ask Handy Andi: Change Your Own Spark Plugs

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Ask Handy Andi: Change Your Own Spark Plugs

Dear Handy Andi,
My car has been a little sluggish lately. A neighbor suggested I change the spark plugs myself before paying to take it to a mechanic. I was too embarrassed to admit I have no idea how to do that. Is it difficult?

Molly, Massachusetts

Changing your own spark plugs is one of the simplest and least expensive maintenance tasks you can perform on your car. And, if it turns out that’s all your car needs, it can save you a lot of money. You’ll just need the correct model of plugs for your car, a decent socket wrench set, and an inexpensive piece of equipment called a “gap tool,” which looks a like silver coin someone attacked with a vegetable peeler.

First, look in your vehicle’s manual to find the correct model of spark plugs. If you no longer have your manual, just ask the staff at your local auto parts store for help. They should be able to find the right ones based on your car’s make and model. Spark plugs are only a few dollars apiece, so purchase enough to replace all of them at the same time. Your manual will tell you how many you need, but you can look for yourself, too. Just pop the hood and count the number of cylinders in your engine, if you don’t already know. Each cylinder will have a protective cap over it with a wire coming from it.

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Ask the parts store staff whether the plugs you’re buying need to be gapped. If so, you can find the gap width information in your owners’ manual, online, or on a sticker under your hood. Use the gap tool to create the correct gap. Just slide the small L-shaped tab at the and of the plug onto the narrowest part of the graduated wedge along the edge of the tool, and slide the plug along the widening edge until you reach the correct width. The tool will force the two electrodes apart to the correct distance.

Once you have your properly gapped plugs, sockets, and socket extender (if needed) in place, you’re ready to begin. Just park your car and allow your engine to cool for several hours — overnight if possible — to avoid burning yourself. Your engine, and especially the spark plugs, can become very hot.

Now, find the correct socket for your spark plugs. Just try to slip your new plugs into several sockets until you find one that it fits into snugly. You’ll need deep sockets to hold the plugs, but don’t worry of they’re not deep enough to reach down into the cylinders. You can use and extension bar to lengthen the distance between the wrench and the socket.

Pop your hood and pull the cap off of the first cylinder. The cap will be attached to a wire. Do not remove any of the other caps at this time. It is important to only remove one at a time so you don’t mix them up.

Use the socket wrench to remove the old spark plug, twisting counter-clockwise to loosen it, just like a screw. Once the old plug is out, use the socket wrench to install the new one, turning clockwise until it is in tightly.

Once the new plug is in place, pop the cap back into the cylinder and press until it snaps into place. Repeat with each of the other cylinders, removing one cap at a time, replacing a single spark plug, and snapping the cap back into place. Clean up your tools, lower the hood, and fire up your engine. If your car runs better, mission accomplished! If not, it may be time to consult a mechanic.

Of course, it’s a good idea to replace your spark plug wires too, while you’re at it. Though not quite as cheap as spark plugs, these wires are also inexpensive, easy to change, and can make a big difference in how well your car runs. I’ll go over that process next time.

Have a question for Handy Andi? Email it to

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1 Bill Hoffman { 09.26.12 at 4:18 pm }

See my comment(s) concerning spark plug wires. Handy Andi has done it again. Today’s vehicles do not lend themselves to easy anything. If you can get to your plugs, fine. If not, pay the “piker”. If your vehicle uses tapered seat spark plugs, tighten no more than 10 inch pounds of torque. Standard plugs (metal gasket) may require up to 30 foot pounds of torque to properly seat and eliminate “missing”. Regardless of plug type, the plug threads should receive a light film of aluminum anti-seize compound to prevent the plug from “welding” itself to the head from operational heat and to also enhance the electrical ground via the cylinder head. After-market plugs have been proven to outperform OEM by a noticeable margin. Don’t be afraid to use them.

2 Cyndi { 07.31.12 at 12:20 pm }

This is one of the best bits of advice my dad ever gave me. He said it was cheap to replace them and better than paying a mechanic to muddle around in your car for a day only to replace them and find that everything is fine. However, some manufacturers have gotten sneaky and put their spark plugs where you can’t reach them without special tools. (I have one such car) so if you can’t reach them easily then ask around for a good neighborhood mechanic. No need to pay crazy dealership prices for something that takes them 20 min max to replace.

3 Jaime McLeod { 07.23.12 at 10:45 am }

Maddie, You’ll be using a socket wrench, so just turn it until it doesn’t want to turn anymore. Don’t try to force it beyond where it feels snug – you could strip the threads, and then you’d be in trouble. You can tell if the plugs are bad if they are discolored – either rusty, calcified (white, powdery residue), or black.

As for your muffler issue, you should talk to a mechanic.

4 Maddie { 07.21.12 at 5:58 am }

You say to put new spark plug in “tightly”… do you mean after it feels snug, to then tighten it more? Can one tighten them too tight? AND- I was told some plugs will last for really long time, maybe not life time of car, but something like 10 yrs?… How can you tell if they are bad?

Another question – my muffler was loose– took me awhile to save $ to get new pipe- during that time the engine light came on… Would that have happened due to muffler? Might it be a simple adjustment?


5 Susan Morrison { 07.18.12 at 9:56 am }

Thank you so much for easy to follow instructions. I’ve always been blessed to have someone else to work on my car when needed, but for simple jobs like this there’s no reason I couldn’t do it myself. Besides, I’m a show-off! I love to set an example for my daughters & granddaughters. When they see Mom tackling jobs that are reserved for the guys, it gives them a sense of independence to realize they can do that too!

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