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H6 Plug Change: Not quite as bad as it is hyped to be.

30429 Views 40 Replies 16 Participants Last post by  lesstutrey
I almost got scared off from reading others' horror stories on the H6 plugs, but I tried it anyway. Tackled this yesterday in just under three hours. I don't think anyone can ever have enough tips on this, so here's mine. A few are probably repetitive:

- Do it from the bottom. I just can't see doing it from the top. My guards are already gone from underneath, so the plugs are right there. No moving the washer fluid reservoir or air intake, killing your back leaning over an engine for hours, or nonsense like that.

- Start with the plug closest to the steering wheel. This is definitely the hardest. If you can tackle this one, you can definitely handle the rest. The passenger's side backmost plug was easier, but that might only be because I had a method down from the other one...I'm not sure if there's actually more clearance.

- You absolutely need a 3" extension or smaller. Bigger ones will do you absolutely no good. I got by with a single 3", a deep socket, socket for the bolt on the coil packs (12 mm?--Can't remember for sure) a swivel adapter, and a standard 3/8 drive ratchet. A smaller extension would have saved me time.

- A swivel-adapter (U-Joint) is somewhat helpful for the back two plugs, but it's not absolutely necessary. I realized it helped a little bit on the passenger side backmost plug, but I didn't use it and still got the driver's side out.

- Definitely use some sort of anti-seize on the threads. I don't know when mine were last done, but some of them didn't turn too easily for quite a few turns and there was evidence of neverseize on those threads. I can't imagine what they might have been like without it.

- As mentioned in other threads, fuel line could be helpful to loosen the plugs but don't rely on it. I couldn't have turned some of mine with it until they were already most of the way out.

- Make sure your ratchet is easy to free from the extension/socket. The reason is you'll need to free it from the extension when the plug is about halfway out, otherwise you won't be able to get the extension out.

- Cold engine is a must. Don't even try it on a hot or warm engine.

- Pliers can be helpful to free the coil pack from gripping the plug if used gently (there's not much room to pull with your hand), but be VERY careful of the plug and wires on the coil pack--it would be bad to destroy them.

- Do it on a warm day or in a heated garage. Numb hands will make the job nearly impossible.

- Be careful of the o2 sensor wires. I could definitely see potential for destroying them with a swing of the ratchet.

All in all, it's really not THAT bad. A lot worse than a V6 for sure, but if you're used to doing your own work give it a try before paying $250+ to have it done. Set aside a few hours (I'd guess just about anyone could have it done in under 4...I did it in just under 3 and am not even all that mechanical). Of course, any number of things could add considerably to that time.

Good luck! Also post any other tips you've got here!
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Awesome advice, especially on the swivel adapters! I have a set, those little guys are priceless when you need them.
Added tip: if you go that deep into maintenance use a decent torque wrench. A stripped thread in the head can be really nasty.
Not sure you want to use a torque wrench on gasketed plugs- isn't the rule 3/4 of a turn after the gasket contacts the head?

That will work, but proper torque specs are always preferred. Stripped threads are not the only worry. The metal crush washer needs to be compressed enough to not enable the plug to loosen after hundreds of heat cycles. A complete "seating" also assists in heat transfer. If a company is going to invest in millions of dollars into R&D for a car I'll pony up $150 for a good set of wrenches. I'm not saying that something WILL go wrong if you don't, just that it is the right way to do it. I think most Subie's are 15 lb-ft
Spark Plug Installation Instructions
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