How to Clean a Spark Plug

Updated on January 5, 2017
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Get More Miles Out of Your Spark Plugs

The spark plug is the life source in an engine. Whether it's a Brigg's & Stratton rototiller or a Chevy 454, the life IS the spark plugs.

Spark plugs are mighty little workers. In my opinion, the spark plugs are the hardest working part in a vehicle next to the tires. They are in constant demand from the very moment the engine is started. They are working, non-stop, until the moment the key is shut off. They are so small, yet they affect several key functions of in a vehicle, such as idling, power, acceleration and fuel consumption.

A set of spark plugs usually lasts about 20,000 to 30,000 miles. This depends on your style of driving. Driving at highway speed, often, will increase the gap faster than driving to the local market several days a week. Under moderate driving conditions, the gap will increase about 0.001in. every 2500 miles; under those conditions the 20,000 rule applies.

You can increase the life of a spark plug by several thousand miles just by cleaning and adjusting the gap.

The procedure in this article does not apply to iridium spark plugs. Sanding an iridium spark plug could potentially damage the tip.

Click thumbnail to view full-size
Copper Spark PlugIridium Spark Plug
Copper Spark Plug
Copper Spark Plug | Source
Iridium Spark Plug
Iridium Spark Plug

Cleaning a Spark Plug

There is a normal build-up of soot, from thousands of explosions a day, that collects on the spark plug. The thousands of explosions each day cause the electrode to slowly wear down. The gap increases, which in turn, effects the fuel economy of the vehicle. Cleaning the spark plug will restore it to like new.

First things, get your ratchet and a spark plug socket together. The spark plug socket has a rubber piece inside of it to protect the spark plug from the hard metal of the socket. You may need an extension in order to seat the socket on the spark plug correctly.

Socket wrench with extension.
Socket wrench with extension.
Remove the boot to access the spark plug...
Remove the boot to access the spark plug... | Source
...use an extension if necessary to seat the socket on the spark plug.
...use an extension if necessary to seat the socket on the spark plug.

Clean the Spark Plug With Sandpaper

Now that you have the spark plug out, using a piece of fine sandpaper (180 or higher) gently sand it.

  • If the gap is large enough, fold the sandpaper in half, slide it between the arm and the electrode and slide it back and forth.
  • If the gap is not large enough to slide folded sandpaper, then use it as is, flat, but remember to flip the paper over to sand the opposing side.
  • Slide the paper between the white insulator and the electrode to clear out any debris that may be in the groove.
  • Blow off the sanded areas with an air hose or a burst of hair from yourself (close your eyes if you opt for the later).

Healthy spark plug in need of cleaning.
Healthy spark plug in need of cleaning.
Slide the sandpaper between the arm and the electrode.
Slide the sandpaper between the arm and the electrode.

Set the Gap

A job isn't done unless it's done right! After sanding the spark plug clean, and blowing out the debris, you need to set the gap.

Refer to your owner's manual for the specifications for your particular vehicle. As you can see in the photo, my vehicle:

  • 1989
  • K series (K is the first letter in the VIN)
  • The engine is a 7.4 litre

With this information we see the gap is 0.035 for my vehicle. Yours may be the same, but check the specifications because it may not be.

Set the gap by running a gapper through the space between the arm and the electrode. The gapper should touch both as it slides through, but it should not stick or click through. If it does stick or click, open the gap by adjusting the height of the arm. If it doesn't touch both armature and electrode, close the gap until it does.

Now your spark plug is ready to be put back into service.

Drive Carefully!

Click thumbnail to view full-size
Check owners manual for gap specificationsGap the spark plugReady to go!
Check owners manual for gap specifications
Check owners manual for gap specifications
Gap the spark plug
Gap the spark plug
Ready to go!
Ready to go!

Tips

  • When replacing spark plugs, replace all of them at the same time.
  • Don't submerge the spark plug in water to clean it.
  • If oil and grease are caked on the spark plug, replace them and have your engine checked; it could be blown or bent rings.
  • Clean one spark plug at a time. Pulling all the spark plug wires off at one time can be confusing when it's time to put them back on. They must be put back at the same spot they came from or you will have major engine trouble if it starts at all!
  • Be Safe and do them ONE AT A TIME.

A Little Bit About Gappers

Below you will find various gappers available at auto parts stores.

The top gapper and the disk type are the most common. They are sturdy and resistant to rust. One side is in millimeters and the opposite side has inches.

The second one down is like the top gapper. It's a disk, very popular and sturdy.

The third one is the prong type. This style provides a separate piece for altering the gap. This is a durable gapper, but seems to catch on other tools in the toolbox or your flesh when working with it.

The fourth one down is a Bonney gapper. The leaves pull out in a fan style. The size is painted onto each strip. Unfortunately they are prone to rust (as you can see) and if you try to steel wool the rust off, the number comes off also!

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Leaf style gapper.Disk style gapper.Fan or stick style gapper.
Leaf style gapper.
Leaf style gapper. | Source
Disk style gapper.
Disk style gapper.
Fan or stick style gapper.
Fan or stick style gapper.

Comments

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  • profile image

    oliverjc 2 years ago

    I remembered about 20-25 years ago my friend's dad cleaning a plug and reusing the plug. As I've definitely and probably have a blown head gasket and on it's way out. Changing the plugs has been my standard each time, I remembered then searched the internet to backup my thinking.

    With this outstanding and informative Hub I got 5 minutes of brilliance for the day. I'm thankful for the posting on this D.I.Y. video.

    A tip of the hat to you Madame!

    Thank You,

    Oliver

  • Msmillar profile image
    Author

    Joanna 4 years ago from Valley Springs

    Hi lesliebyars, thank you!

  • Msmillar profile image
    Author

    Joanna 4 years ago from Valley Springs

    Thanks hardlymoving! Too true, Do Not File Iridium plugs, it could potentially ruin the tip. Plugs are generally pre-gapped but this hub is referring to plugs that have been driven 20,000 - 30,000 miles already, increasing the gap out of its recommended range. Filing a new spark plug, out of the box, would be simply silly. I don't agree that, "Only garden equipment use the old style copper plugs..." as a mechanic I see a lot of engines, of the average Joe, everyday, and they use Platinum and some Copper plugs. 1994 saw the first iridium plug, used in foreign made vehicles, but not yet used in the mainstream of auto manufacturing. Their popularity has grown because of their high melting temp allowing for longer life and their corrosion resistance. Keep in mind they do not increase the power over any other plug. Thank you for keeping me on my toes! :)

  • profile image

    lesliebyars 4 years ago

    Nice hub. Thanks for Sharing this information my friend.

  • hardlymoving profile image

    hardlymoving 4 years ago from Memphis, TN

    Today's auto manufacturers provide Iridium spark plugs as standard equipment on new cars and they're good for 100,000 miles. They replaced Platinum plugs which were usually good from 60,000 to 100,000 miles. The Platinum plugs replaced the copper types which were good for maybe 10,000 miles depending on whether they were used in forced induction applications. Both Iridium and Platinum plugs, in most instances, are pre-gaped, and re-gaping and cleaning is not recommended. Only garden equipment use the old style copper plugs that should be seasonally cleaned and its gap checked.

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