Replacement and Maintenance of Spark Plugs

This video explains how to replace the spark plugs on a Subaru Forester and how to maintain the electrical device. After opening the bonnet, remove the air intake and the intake manifold.

Also, remove the airbox by unscrewing a bolt with a 10 mm spanner. Take off the windscreen washer reservoir and disconnect two plugs for the washer and two engine plugs.

Leave the plugs resting on the bumper. The spark plugs are now accessible.

Firmly grip the top of the spark plug and make a forward-backward motion to free it. Extract the spark plug (it can be unscrewed by 45 degrees without resistance). At this point, there’s a problem: the well seems to be leaking oil. Oil ends up on the spark plug insulator (still in good condition).

The same happens with the cylinders: a new set of valve cover gaskets is needed! First, clean all traces of oil. If the oil leak has been present for too long, it may have damaged the leads. So, thoroughly remove the oil traces using cleaning products as indicated in the video mixed with water.

Use dielectric grease for spark plugs on the bottom part of the ceramic body (insulator), spreading it well with a screwdriver. Use silicone grease to lubricate the ends of the spark plugs.

Use the spray indicated in the video to clean the wells. Add a small tube to better direct the spray.

Spray the liquid freely. Then channel some compressed air. Choose the appropriate spanner to remove the worn spark plug.

Compare it with a new spark plug: the electrode of the new spark plug appears with sharp threads. A new spark plug has the electrode perfectly centred, the threads plated, and the internal cores in good condition.

Inspect the old spark plugs for ash or chemical residues. Burnt oil residues and coolant consumption are often a problem for spark plugs.

Finally, do not overtighten the spark plugs.