How To Change Spark Plugs

Expect spark-plug work to be tedious. If this is your first time, plan 3 or 4 hours after engine cools (or 1 hour on several days), allowing 15 minutes per plug. It is harder than changing air filters, fixing flat tires, or starting a mower.

Consult your vehicle's manual. Look up where your spark plugs are, how many you have, the correct "gap", and the size socket needed to remove them. Also write down the vehicle's make, model, and year. The gap can also be found on the emissions label under the hood.

Visit Complete Auto Parts. Find (either by looking up in the provided reference book or by asking an employee) the correct spark plugs for your vehicle. The store also has socket wrenches, plus spark-plug sockets (with gasket), and socket-extension rods or swivel-joints to reach recessed plugs.

Find out (from the reference book, the packaging, or the employee) if these spark plugs need to be "gapped". Some modern plugs should not be gapped (but others can have different gaps, depending on use in either 6-cylinder or V-8 engines, etc.).

Park vehicle, turn off the engine, and open the engine compartment, to cool for hours. (WARNING: After running a car for a long time, the spark plugs can be the hottest part of engine! While it can require several hours to cool enough, it can require several weeks to heal burnt skin.) Especially with aluminum-head engines, let cool to room temperature to reduce the probability of damaging the threads.

Take (if needed) a wire-gauge spark plug gap tool and adjust the distance between the two electrodes. Between the electrodes is where a spark is made. One electrode will be an L-shaped piece of metal (hook), the other a metal prong centered directly across from it. Set the gap between the two electrodes, from .028-.060 inch, such as .035/.040 /.043 /.050, as in book (see Tips below).

Collect tools & new plugs (perhaps in a tool-tray). Remember which direction the socket-wrench switches to reverse/unscrew: wrench might not be visible when working back plugs.

Check fit of new plugs inside wrench-socket gasket. If new plugs stick to rubber gasket, consider removing gasket with screwdriver in square hole, to just use tape. Like taping screws to a screwdriver, the socket can be taped to spark plugs (not the threads) with scotch tape, for easy release once inside the engine. Otherwise, have pliers to pry the socket off new plugs once installed.

Locate (with the help of your manual or a repair manual for your vehicle) the distributor spark-plug cables/wires. The number of wires will be equal to the number of spark plugs your engine has. Often these wires are red or black, and will be equally divided on opposite sides of the engine.

Using masking tape, mark each of these wires for where they connect. Don't rely on memory: if interrupted, easy to forget, and engine can run rough with crossed plug wires. For 8 cylinders, deducing plug connections is almost impossible (120 choices for 5 wires) -- in that case you must contact an expert or study wiring guides.

Remove each spark-plug cable, pulling the caps (to avoid breaking cable wires). Caps should come loose by very intense twisting/pulling (avoid jerking/hitting fingers).

Using compressed air, pressurized engine cleaner, or a brush, clean all debris from around the plug.

Using a spark-plug socket, remove each plug from the engine, and replace each with a new spark plug. Don't over tighten (usually just 1/16 turn, after finger-tight).

Replace the spark-plug cables on the same plugs they originally came from, and remove the masking tape.

Remove tools near engine (beware the moving belts), close your engine compartment, and start your vehicle.