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How To Put Spark Plugs In

Spark plug

A regular routine of maintenance for gasoline engines is spark plug replacement. Normally, this is part of the regular "tune up" process which replaces and adjusts several things on the vehicle's engine to "tune" its running for maximum fuel efficiency and output.


Traditionally, spark plugs are replaced about once a year or every 10,000-12,000 miles. Most mechanics will replace spark plugs every 3rd oil change. These numbers/intervals are adjusted according to usage, with vehicles operating mainly in city (stop-and-go) traffic requiring a change more often.

Newer vehicles often have much longer intervals between changes, so check your manufacturer's requirements before deciding on an interval.

Steps to Changing Spark Plugs

Changing out the spark plugs is an easy home mechanic's task you can DIY. First, open the hood of the car, check the fluid levels and other routine things you should check every time you are under the hood.

You will need the following items:

  1. 4, 6, or 8 spark plugs of a type specifically recommended for your vehicle make/model and its engine. On newer vehicles, this is very important as engines are now pre-tuned for specific plugs and "upgrading" can actually harm your car.
  2. Wires to replace the current plug wires on your vehicle, unless you have lifetime wires which should require no replacement. Always buy the best you can afford with these wires.
  3. A socket wrench or turning handle.
  4. A spark plug socket sized for your plugs (there are two standard sizes: 13/16" and 5/8". They will have a rubber insert for gripping the porcelain portion of the plug to protect it and allow for easy removal. Most mechanics have two of each type of socket, one with the rubber removed to facilitate easier extraction once the plug has been put into the vehicle.
  5. Extensions as necessary to reach your plugs with your socket and wrench.
  6. Recommended on aluminum cylinder heads: engine head spark socket cleaner for lightly cleaning the threads of your engine cylinder head's spark plug holes.
  7. Other tools for removal of engine covers or other parts that may be required on some vehicles.

Follow these steps:

  1. Disconnect the negative battery terminal so that no power can flow through the electrical system.
  2. Locate the spark plugs on your vehicle's engine by tracing the spark plug wires from the distributor or EFI/computer. They are large, round wires and there will be four, six, or eight of them (one plug per cylinder, one wire per plug). Be sure you know where each plug is located and where the wires terminate at either end (one in the plug, one in the distributor/controller).
  3. Disconnect one wire from its spark plug and remove the wire. Find the like-length replacement wire in your new wire kit and set it aside.
  4. Remove the spark plug you've exposed, carefully extracting it.
  5. Check the spark plug size and gap with the new plug to replace it. Be sure they are correct before proceeding.
  6. Using your thread cleaner tool, carefully screw it in and back out of the spark plug hole to clear the threads and remove any nicks or dents in the aluminum (if appropriate). This helps prevent cross-threading and future serious problems.
  7. Carefully put new plug in place, turning lightly until it is properly seated on the threads of the cylinder head. Tighten to specified torque or until lightly hand-tight. DO NOT OVER TIGHTEN!
  8. Replace spark plug wire removed with new wire.
  9. Repeat for each plug until all have been replaced.

Normally, during spark plug replacement, the interval would also call for replacement of the distributor's cap and rotor (if any).

Changing out spark plugs is easily done at home on most makes and models. Some newer models require very expensive plugs, but need changing less often. Again, be sure you are purchasing the correct plugs for your vehicle!