How to Change Spark Plugs

Is it time for your vehicle to get a spark plug replacement? As you can imagine, changing spark plugs on your own can be a bit nerve-racking the first time around, but once you have done it a few times, you will see that it’s not so bad – unless you run into complications. That is why we always recommend having a professional mechanic replace your spark plugs, just in case there are complications you aren’t aware of. However, if you are going to be replacing spark plugs on your own, follow our short “How to Change Spark Plugs” guide below for some additional guidance. If all goes smoothly, changing spark plugs should take around an hour (for a four-cylinder engine) to complete. 

Tools that can make changing spark plugs easier are a gap gauge, needle-nose pliers, rags, socket/ratchet set, spark plug wire puller, swivel socket, and a torque wrench. You will also need new spark plugs and an anti-seize compound. Once you have everything you need to get the job done, it’s time to learn how to replace spark plugs.

Step 1: Locate the Spark Plug (Check owner’s manual if unsure)

Open the hood of your vehicle and look for a bundle of 4-8 wires leading to different points on the engine compartment. The spark plugs will be located at the engine end of these wires, under the plug covers that are attached to them.

• For most 4-cylinder engines, the spark plugs will be located on the top or side of the engine.
• For most inline 6-cylinder engines, the spark plugs are located on the top or side of the engine head. However, on V6 and V8-cylinder engines, the plugs should be separated evenly on each side of the engine.
• In some vehicles, you may have to remove an engine cover before you can see the spark plug wires. Once you remove the engine cover and expose the spark plug wires, you should be able to trace them back to find the plugs themselves. When in doubt, remember to check your owner’s manual to determine where the spark plugs are, how many there are, the correct “gap”, as well as the size socket needed to remove them. 

Step 2: Let the Engine Cool Down

If your vehicle has been running for a while, be sure to allow the engine to cool down before changing spark plugs as the plugs, the entire engine, and the exhaust system are likely very hot. Be sure to only remove the spark plugs when the engine and its components are cool enough to touch with your bare hand. If your car has not been running, feel free to skip this step.

Step 3: Start Removing the Spark Plugs

Pull the wire plug from the engine by gripping it from the bottom and carefully work it off to reveal the spark plug. Once the spark plug is revealed, use a fitted socket wrench with the extension bar and ratchet to remove the spark plug from its housing. Be sure to do this slowly and cautiously so you don’t create a bigger issue for yourself.

• If you are removing them just to check if they need replacing, simply remove one spark plug and check the gap. If contacts show signs of being burnt out, they should be replaced. 

Remember to remove the plugs one at a time and to help keep track of the order. Spark plugs generally fire in a specific order, so crossing a wire to the wrong plug can make the engine run oddly if at all. This can also cause damage to your engine.

• To further avoid the potential for crossing a wire, you can label each wire numerically, then give the corresponding plug the same number. This will help you remember what goes where when the time comes to insert the new spark plugs and reconnect the wire plugs.

Step 4: Measure the Gap

Once all of the old spark plugs are removed, it is time to measure (and adjust if necessary) the gaps of the new ones. This gap space should be a specific measurement between .028-.060 inch, with some wiggle room depending on the particular set of plugs and your vehicle. Most modern plugs come pre-set according to the spark plug’s model number and their application, but it is good to always double-check. As always, when in doubt refer to your owner’s manual to find out the optimum distance for your spark plug gap.

• If the distance of the spark plug gap is higher than it should be, you can either try to change the gap by gently tapping the plug on a wooden surface until the desired measure is reached or you can simply buy new plugs.

Step 5: Consider Cleaning Wire Terminal

Once your new spark plugs are ready to be installed, consider cleaning the threads before inserting the new spark plugs. When the spark plugs are being replaced, it is a good opportunity to check the wires for wear and clean up around the wire terminal. Use a wire brush or compressed air to clear the area of dust and debris. If wires look to have too much wear and tear, they might also have to be replaced. 

Step 6: Insert the new plugs

Finally, it is time to insert the new spark plugs. Using a spark-plug socket, remove each plug from the engine (if you haven’t already), and begin replacing each with a new spark plug. Tighten carefully to just past hand-tight only. Do your best to never over-tighten the plugs as the threads on the head of the engine can be easily stripped.  If unsure about this step, you can find the torque specification for the spark plugs in your vehicle’s service manual. Once the spark plugs are secured, remember to replace the spark plug cables on the same plugs they originally came from.

• If you are installing them in an aluminum engine, try putting a small amount of anti-seize lubricant on the plug threads. The anti-seize will help prevent a reaction between dissimilar metals. 

Now that you know how to change spark plugs, you may be thinking, “how often do you change spark plugs?”. Thankfully, spark plugs are pretty durable and don’t need to be replaced too often. That said, the general recommendation is to change your spark plugs every 30K to 90K miles or so. However, every engine may differ depending on how often the vehicle is being used. That being said, knowing when to change spark plugs isn’t always easy, so to be safe, be sure to review your owner’s manual or speak with a professional for details on when to replace the spark plugs for your specific vehicle. If you prefer to have one of our expert mechanics here at GT Auto change your spark plugs for you, give (385) 497-6342 a call to schedule an appointment today! We would be happy to help you change spark plugs and get your vehicle back on the road and running how it should be.