Covering the basics of spark plug maintenanceWritten by Nick Shultz | | firstname.lastname@example.org
I received an e-mail from a reader asking how to change the spark plugs in his car. Replacing the plugs on today’s vehicles does deserve some thought. The fact is that finding the spark plugs on some of today’s engines can leave the do-it-yourself home mechanic lost. Let’s cover the basics.
Whatever the configuration of your engine, it may very likely have aluminum cylinder heads. If that is the case, make sure you remove and reinstall the spark plugs when the engine is cool. It doesn’t have to be cold, but it shouldn’t be warm and most definitely not hot. Trying to remove the spark plugs while the engine is hot could very likely result in damaged threads in the soft aluminum cylinder heads. Repairing the damage could require removing the cylinder heads or at worst, replacing them. Replacing the cylinder heads is a very expensive and time-consuming job.
Even if your engine incorporates cast-iron cylinder heads, you still want to remove the plugs when the engine is cool.
If you don’t own a socket that is specifically designed for spark plugs, you should pick one up while you’re at the parts supplier purchasing your plugs. Do not use a regular socket that fits the plug. Use the special-purpose spark plug socket only. While you’re at the parts house, you should pick up a small amount of anti-seize compound as well. We will discuss why in a moment.
Let’s locate your spark plugs. You may likely have an ignition system on your vehicle that does not incorporate a traditional spark plug wire. This technology is referred to as coil on plug. The spark plug will be located beneath the coil. There will be one coil for each spark plug. After removing the coil, you will have access to the spark plug.
The plug itself may be several inches below the coil pack. It will be necessary in most coil-on-plug applications to use a 6-inch extension on top of the spark plug socket in order to reach the plug located deep in the cylinder head. Use a firm, not jerky, circular motion in a counterclockwise direction and remove the plug. Do the same for each spark plug.
Spark plugs in other type of ignition systems can be located by following the spark plug wire to the plug. Remove the spark plug boot carefully from the spark plug and, if necessary, mark it so you will be sure and put it back on the same spark plug it came off of. Do the same for every plug. Remove each plug as described above.
Organize the spark plugs as you remove them in a manner that will allow you to identify the cylinder that the spark plug was removed from. After all the plugs are removed, inspect them. You’re looking for plugs that have a different color than the rest. The off-color plugs indicate some type of a problem in the particular cylinder they came out of. If you don’t have experience reading spark plugs, you might want to take them to your local technician and have him or her read them for you.
The next step would be to gap all the new spark plugs. Make sure that the gap is equal on all the plugs and that it is set to the manufacturer’s specifications. During this procedure, you should also make sure that the outer electrode is centered as evenly as possible over the center electrode.
After the plugs are gapped, then you should take a small amount of the anti-seize compound you purchased and apply it to the bottom two threads of the new spark plugs. Make sure you use a small amount and only apply the compound to the bottom two threads.
Once the plugs are ready, you can begin reinstalling them into the cylinders. I have found that a 6-inch piece of vacuum hose attached to the top electrode of the spark plug enables you to start the plug into the female threads of the cylinder head without fear of cross-threading the plug. I suggest you use this method to get the plugs started. Once you have the plug started into the cylinder head then go ahead and run them semitight into the head. After all the plugs are installed in this manner, go back with a torque wrench and torque the plug to the manufacturer’s recommended torque setting. Proper torque of the spark plug is important.
Reconnect any of the spark plug boots or ignition coils you may have removed and start the vehicle and make sure it doesn’t miss-fire. Once you’re sure the vehicle is idling and running properly, take the vehicle out for a test drive. It is important to operate the vehicle under a normal and a heavy load to determine if the plugs are indeed operating as designed. Once you are satisfied that everything is OK then return to your shop.
A simple job that many take for granted can turn into a nightmare if done improperly. Good luck with your wrenching.
Nick Shultz is an instructor of Automotive Technologies at Owens Community College. He is an arbitrator for the Better Business Bureau who specializes in cases involving the Ohio and Michigan Lemon laws. He is a certified master automotive technician by ASE, General Motors Corp. and Ford Motor Co. Shultz will take automotive technical questions from readers at email@example.com.