Skip to main content

How to Clean a Spark Plug

  • Author:
  • Updated date:

After working on cars for so many years, I have found that some parts don't need to be replaced. They just need a quick cleanup or repair!

Spark plugs are mighty little workers.

Spark plugs are mighty little workers.

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 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 0.001 inches every 2,500 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.

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, affects the fuel economy of the vehicle. Cleaning the spark plug will restore it to like new.

First, 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.

Clean the Spark Plug With Sandpaper

Now that you have the spark plug out, using a piece of fine sandpaper (180 grit 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 latter).

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!


  • 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!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: What is the point gap for a vehicle when adjusting the spark plug gap?

Answer: The point gap for an individual vehicle can be found online or in the repair manual for that vehicle. The larger the gap, the longer it will take for the spark to fire.