How To Change Your Vehicle’s Spark Plugs


Maintenance is an extremely important factor in a vehicle’s lifespan and performance. Many maintenance items and procedures that are recommended and are rejected by customers end up causing major problems and repair bills in the future. Between all the fluid flushes and filter changes that will inevitably be offered to you at the shop over time, one that many people overlook and simply ignore is spark plug replacement. The spark plugs are responsible for consistently igniting and efficiently burning the fuel in the engine. When spark plugs wear out, the spark becomes weaker and may not fully burn the fuel in the cylinders or ignite it at all. Vehicles with old spark plugs may exhibit poor gas mileage, lack of power, rough idle, or even hesitation and misfiring. That being said, it is important to change your vehicle’s spark plugs within the recommended service interval to keep your engine running in excellent condition and at maximum efficiency.

The first step to take in this process is to find out what the service interval is for the spark plugs on your particular vehicle. The easiest way to obtain this information is to call a dealership that specializes in your make of vehicle and ask a member of the service staff. Some vehicles even include detailed service schedules in the owner’s manual, but many do not. If you have determined that your vehicle is in need of spark plug replacement, the next step before breaking the tools out is to buy the correct spark plugs for your vehicle. There are many different types of spark plugs that utilize different types of metals and electrode designs, and it is very important that you install plugs of the same specifications of those that you removed. While you still have the dealership on the phone, ask to be transferred to the parts department to inquire about which type of spark plug is specified for your vehicle. There are many sources from which to buy spark plugs, but it is important you get the correct type with the correct fitment for your vehicle.  Once you have the correct spark plugs, it is recommended that you buy or rent a spark plug socket set and a torque wrench. Spark plug sockets contain a rubber insert that helps prevent the porcelain top of the plug from breaking off when removing or installing it. The torque wrench will allow you to install the new spark plugs to the specified torque, or turning force. Both tools are recommended but not absolutely necessary to complete the job. A spark plug gapping tool may also be necessary depending upon which type of plugs you are using. Some plugs come pre-gapped and some require gapping. Be sure to get this information when you buy the plugs. If needed, a spark plug gapping tool can often be had for under five dollars.

Now that you have everything you need, you are ready to get to work. The first thing you need to do is determine the number and locations of the spark plugs on your engine. There is typically one spark plug per cylinder, with the exception of the Dodge Hemi engines, which use two plugs per cylinder. Before you begin removing anything, be sure that you can access all of the spark plugs without issue. A few vehicles have spark plugs that can be extremely difficult to change and are best left to the hands of a professional technician. If everything is giving the green light, you will need to remove either spark plug wires or the ignition coils depending on the design of the ignition system on your vehicle. There will either be one wire per spark plug extending from a central distributor, or an individual coil for each cylinder. Remove all the wires or coils to expose the spark plugs. If you are dealing with a distributor system and spark plug wires, it may be a good idea to mark all of the wires so that you ensure they are returned to their original locations. You will know very quickly if you accidentally crossed wires upon completion.

The next step is to remove the spark plugs from the cylinder head or heads. Slide the spark plug socket snugly over each plug. It should not take a terribly large amount of force to break the plugs loose and thread them out. If you are using a regular metal socket for this, be extremely careful not to twist the plug at an angle and break the porcelain top. Once the plug is broken loose from the threads in the cylinder head, it should turn out with ease. If a plug is proving harder than all the rest to break loose or is not turning out easily, first try applying lubricant to the threads. If no success is had, do not continue because you may break the plug or ruin the threads in the cylinder head. If you run into a situation like this, don’t panic. Simply thread the plug back down or leave it be if you were not able to break it loose and have a shop look at the specific plug you were having trouble with. Issues like this with spark plugs are not common but it is very important to recognize a problem and prevent any damage to the engine.

Before installing the new spark plugs, you may need to set the gap between the electrode and the ground prong. Proper gap is crucial to plug and engine performance. If your spark plugs came pre-gapped as mentioned above, you will not need to worry about this and can move on to installing them. If gapping of the plugs is required, follow the instructions with the gapping tool to properly set the gap on all of the new spark plugs.  Once this is done, you may carefully install the new spark plugs. A spark plug socket makes this step easier as well, because the rubber insert in the spark plug socket will hold the plug in place while you lower it down into the head.  If you are using a torque wrench, set the torque on all plugs to the proper specification. It is acceptable to install the spark plugs without a torque wrench, however take care that the plugs are snugged down well and that the same amount of force was used to tighten each one. Now simply reinstall the ignition coils or spark plug wires in their respective positions and start the vehicle. The engine should run smoothly without misfiring. Test drive to vehicle to ensure that no issues have arisen.

As stated above, you may notice improved gas mileage, power, and running stability from installing new spark plugs depending on the amount of wear on the old parts. If you notice no difference, then you’ve successfully prevented those unwanted symptoms of worn spark plugs for many thousands of miles to come. Either way, changing your vehicle’s spark plugs is a worthwhile investment of time and money to help keep your vehicle in top running condition for many years.

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