Sunday, August 20, 2017

2012 Impreza Spark Plug Replacement

New spark plug on top, old on bottom.
The recommended replacement interval for my Impreza's spark plugs is 60,000 miles. The OEM plugs are NGK SILZKAR7B11. The engine bay is a little tight, so the service manual specifies removing the battery and air cleaner case to make some room.

Driver side: battery, mounts, and padding removed.
Passenger side: intake, air box, and filters removed.
To get at the spark plugs, remove the connector and screw holding the coil pack.

The coil pack screw has a 10mm hex head. The electrical harness has a single clip on the outer side.
The whole affair is a knuckle-buster. I used a wobbly setup to help get at all the screws.

R-L: ratchet, extender, universal joint, socket
Once the ignition coils are off, the ports look like this

Driver's side
Use a 14mm socket to unscrew the spark plugs. I didn't have a spark plug socket, so a piece of 3/8" hose works as an extraction tool.

3/8" ID vinyl tubing fits over the spark plug stem
Assemble in reverse. When replacing the plugs, apply dielectric grease to the boot of the coil pack and onto the ceramic stem of the plug.


A bit of anti-seize on the spark plug threads will prevent corrosion for the next change.


Torque the new plugs down to 12.5 ft-lbs. The coil pack torques down to 8.9 ft-lbs.

Ignition coil and spark plug

Passenger side