NAPA Auto Parts NAPA Montréal
2085 AV HAIG
(514) 351-4210
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  • Spark plugs replacement


4 spark plugs and their electrode

Difficulty: Easy to medium
Duration: Depends on engine's design
How often: See your owner's manual

Why replace your spark plugs?

Spark plugs are the heart of your vehicle's engine. For maximum fuel economy and peak engine performance, your spark plugs should be replaced every 30 months or 30,000 miles (48,000 kilometres). This may vary depending on the type and model of your vehicle. This brochure will help you replace your spark plugs quickly and correctly. Although replacing plugs isn't usually difficult, be sure to READ all instructions provided.



  • Spark plug wrench or a spark plug socket and ratchet
  • Spark plug gap gauge
  • Torque wrench (optional)
  • Rag or brush
  • 5/16" rubber hose of approximately 6" long


Proper maintenance and service procedures are vital to the safe, efficient operation of all motor vehicles, as well as to the safety of the person performing the work—you.

Whenever you're working on your vehicle, we recommend that you follow these important safety rules:

  • Do have a first-aid kit handy.
  • Do be careful when working around hot or sharp objects.
  • Do follow the manufacturer's instructions for all products.
  • Do use safety stands under the frame or drive-on-ramps if you must raise your vehicle.
  • Don't run the engine without proper ventilation.
  • Don't smoke when working around the engine.


READ these instructions completely before you begin:

Purchase new plugs that are the right size and heat range for your specific engine (consult a spark plug manufacturer's guide). Never rely on cross-references. NAPA representatives can help you find the right spark plugs.

Remove the spark plugs

Figure 1

  • Allow the engine to cool completely before attempting to remove the old plugs. This is particularly true if the engine has aluminium cylinder heads.
  • Gather together all the tools and equipment you'll need before you start.
  • Adjust the new plugs to the proper gap beforehand. The correct gap for your vehicle's engine can be found in the owner's manual.
  • To avoid mixing up the spark plug wires, it's a good idea to remove and replace one plug at a time or use tape to label each wire.
  • With the engine cool, carefully remove the spark plug wire from the end of the spark plug by pulling the rubber boot. Do not pull the wire itself. If the boot sticks, use a twisting motion to pull the boot and plug wire free(see Figure 1).
  • If compressed air is available, use it to blow any dirt away from the spark plug area. Otherwise, clean off the old plug and the area around it with a rag or small brush. This will help prevent any foreign material from falling into the cylinder when the plug is removed.
  • Remove the plug by turning it counter-clockwise with a spark plug wrench or a spark plug socket and ratchet. If the plug is hard to remove, use a small amount of penetrating oil to help remove it.

Adjusting the gap of the new spark plug

Figure 2

  • Set the recommended gap in the new plug with a spark plug gap gauge (the correct gap can be found in your owner's manual). Insert the proper thickness wire or feeler between the inner and outer electrodes at the tip of the plug. When properly gapped, the wire or feeler should slide between the electrodes with a slight drag. If the gap is incorrect, gently bend the outer electrode slightly until the correct gap is achieved(see Figure 2).
  • Make sure that the outer electrode is centred directly over the inner electrode. If it's not, align the two by gently bending the outer electrode.

Checking the Cylinder Head Threads

  • Visually inspect the cylinder head threads. They should be in good condition, clean, and free of dirt and debris. This new spark plug should freely screw into the cylinder head by hand. Any binding of the plug is an indication that there's a problem. Remove the plug and inspect the threads.

Installing the new spark plug

  • Make sure that the area around the spark plug port is clean. Wipe the seat with a clean rag to ensure proper contact between the new plug and the seat.
  • Insert the plug into the spark plug hole by hand and turn it clockwise until it's snug. If the spark plug hole is hard to reach, try attaching a short piece of 5/16" rubber hose to the top of the plug and use it as an extension to help reach the hole.
  • After installing the plug by hand as far as it will go, firmly tighten it with a spark plug wrench or socket. It's a good idea to use a torque wrench, if one is available, to ensure that the plug's properly seated. DO NOT OVER-TIGHTEN. Remember, you'll get an accurate torque reading only if the spark plug and cylinder head threads are clean and dry.
  • Reattach the plug wire to the new plug. Use a twisting motion on the boot until it's firmly seated on the top of the plug.
  • Repeat the above steps for each plug you're replacing.


  • Follow these instructions carefully. Read and be sure you understand them before you begin.
  • Gather all your tools and supplies before you begin.
  • Allow plenty of time to do the job so you don't have to hurry. Remember that these are general instructions. For more detailed instructions pertaining to your specific vehicle, consult an appropriate repair manual.
  • Safety is important whenever you're working around machinery. Beware of hot objects, sharp instruments and hazardous materials.
  • Don't substitute tools unless you're sure you won't compromise either your safety or the performance of your vehicle.
  • If you have any questions about repair and maintenance, contact your local NAPA Auto Parts store. Find the nearest NAPA Auto Parts location.