Changing the spark plugs on your Subaru Forester is a rewarding and cost-saving long term measure to ensure your Subaru is running at its peak performance level. While the Subaru owner's manual recommends changing your spark plugs every 60,000 to 100,000 miles, changing them more frequently can prevent engine problems and keep your vehicle running smoothly. Changing them yourself will save you money and time, as well as increase your level of confidence with repairing your own vehicle.
Locate your spark plugs. If necessary, refer to your Subaru Forester owner's manual for spark plug location and model-specific additional information. In most vehicles, the spark plugs should be in the centre of the engine, on either side of the block.
Remove one of the spark plug wires from a spark plug. To remove the wire safely and prevent damage to the wire or the plug, grip the spark plug wire at the base of the wire, where it meets the spark plug. Pull the wire straight out, being careful not to put pressure on the wire itself or pull at an angle, as this can damage the wire.
Lower your socket into the spark plug chamber, and rotate the socket counterclockwise until the socket locks into place around the spark plug. Rotate the spark plug counterclockwise until it comes from the engine, then carefully lift it out to remove it.
Check the spark plug for signs of extreme damage, as serious wear and tear on spark plugs beyond the typical blackening can be a sign of engine and ignition troubles. If you discover these signs during spark plug removal, take the plugs and your vehicle to a local mechanic for further service.
Apply a light coat of anti-seize compound to the threading of the new spark plug. Insert it in the socket and lower it into the spark plug chamber. Rotate it clockwise until it begins threading smoothly, then tighten it until you meet serious resistance. At this point, give the spark plug one-eighth of a turn to give it the proper torque.
Reattach the spark plug wire to the new spark plug. Be very careful to only work with one spark plug and wire at a time so you do not place the wires in the incorrect order. Mismatched spark plug wires can cause severe engine damage.
On some Subaru Foresters, the spark plug removal is much easier if you remove the air cleaner box. Refer to the owner's manual for the location of your air cleaner box and additional removal instructions. A special spark plug socket is a cheap and useful tool which is padded to protect the spark plugs during installation and removal. They are often magnetised to allow easier control of the spark plug. Replacing your spark plug wires as well is another excellent way to save money and increase performance, especially if you notice wear or corrosion on your wires while replacing the spark plugs.
Never perform this repair when the engine is running. Always allow the engine to cool before working with the spark plugs.