How to replace Spark Plugs – Subaru Outback 2008

I drove over 30,000 miles my Japanese-made all-wheel-drive machine, which means it requires some maintenance. As far as I know, the only car maker that also covers maintenance within warranty period is BMW. Should I spend $500 at dealer shop for 30,000 miles service? No way. Should I sell my ride? The new model looks more attractive and roomier, and the resale value of my ride is pretty good. Though I was pretty tempted, I decided to keep it for now. Instead I will do the maintenance by myself. Okay, let’s list the items:

Coolant, Air filter, Spark plugs, Transmission fluid, Brake fluid

Replacing fluid would be rather straightforward but how can I change spark plugs? According to the reliable service manual (of course, internet…), it is pretty simple if I have proper tools. Well, I bought tools and tried to do it finally, but I realized it is NOT that simple!! Why? Subaru has a unique engine design, so-called boxer engine. The cylinders are horizontally located two on the left and the other two on the right. This makes the access to the spark plugs quite difficult. Let me go through this step-by-step.

The tools needed: torque wrench (21 N-m/15.5 ft-lb), 3/8″ spark plug socket, 3/8″ socket extension, 3/8″ socket adapter, 3/8″ ratchet, and screw driver.

The parts needed: spark plugs (NGK FR5AP-11).

Disconnect the ground cable from the battery for safety. You need to remove the air filter case and the connecting tube to access the right side (of the car) spark plugs.

The air filter is located right behind the right headlight – the black box with two finger clamps, which is connected to the engine via a semi-flexible tube. Release two finger clamps (by hand) and a ring clamp (using screwdriver) of the air filter case, and remove the case and the filter. The image below shows when it is removed.

Then, remove the flex plastic tube connection in the same way. The image below shows when both parts are removed.  Now you can access the right side socket plugs. There is nothing to remove on the left side (of the car) to access spark plugs.

Next, find the socket plug cord and boot (see the black rubber sticking out of engine block?) and remove them. The boot is designed to help removing it by hand, but you will need a lot of force. You should not pull the cord itself.

The image below shows the cords and the boots on the left side of the car. See how easy they can be reached?

Once you remove the boot with the cord, grab spark plug socket, connect socket extensions, and insert it to the bore. See the image below.

I use the below combination to remove the spark plug.

See the difference. New vs. old.

After switching the plugs with new one, carefully insert through the bore and hand tighten it first. Then set the torque wrench to the specified torque and tighten it.

The left side is a little more difficult just because of the tighter space.

I had to use slightly different combination for the same reason. I just switched two adapters and it worked.

See how the long torque wrench is connected to the socket adapter.

Once you replace all four plugs, plug in the cord boots, connect the tube and the air filter case, and finally connect the cable on the battery. I was a little bit nervous before I started the engine, but it worked very nice. Carefully hear the engine sound and test drive.


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