I changed the plugs on my 2012 Outback (H6) and have a few observations.
First is the price ($250 to $320) for hiring a professional mechanic may be a wise investment even if you are familiar this task.
It is a very arduous task, it took me about 7 hours to complete. If your hands are large you may especially want someone else to do this, it is possible your hands won't even fit. There is barely 1" space between the spark plug hole and the frame rails and the plugs have 1" of thread.
If you wish to bond with your Subaru, here are some pointers I learned along the way:
1. Buy quality Iridium tips plugs, they last longer. The OEM plugs at 60,000 miles still looked in good condition though the gaps had increased to .060+.
2. You will need an assortment of sockets, extenders, universal and or flexible, 1/4", 3/8" and possibly 1/2". You will also need a torque wrench. The factory Subaru manual shows the use of a flexible spring type socket extender, this is only useful after the plug has been initially loosened.
3. Wait until your engine is cold before you start, these 1" long plugs have 3/8" of thread which extend into the combustion chamber and that section is burned rough. It is risky to unscrew such a plug through a hot aluminum cylinder head. Shucks you'll burn your hands anyway if you don't wait for a cold condition. NOTE: the 4 cylinder Subaru uses plugs with 5/8" of thread which don't extend into the combustion chamber therefore I assume they are easier to manage.
4. Each plug has its own ignition coil which is held in place with a single bolt.
5. A 1/2" socket an breaker bar may be needed to loosen the plugs, after that a flex extender or universal sock may be used. Several combinations of sockets and extenders will be needed and each cylinder if probably require its own combination.
6. Reinstalling is not just reverse order, first check the plug gaps (.039-.043") to make sure they are all the same, next apply thread lubricant (e.g. Never Seez or similar compounds.) to protect the aluminum threads for the next plug change.
7. Spray something like silicone lubricant onto the rubber in the Spark plug socket, this is simply to make it easier to remove the socket once the plug is in place.
8. Torque Spec: 15.5 Ft-lb dry 10.9 Ft-lb greased.
9. After total reassembly wash up and apply band-aids as required to your wounded hands.
10. PDF files attached for your convenience.
2012 Subaru H6 Spark Plugs.pdf
