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

30434 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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How many miles on the plugs you removed? What made you feel they needed changing? What plugs did you go back in with?

I'm one of those people that try to talk myself into paying someone to do it. Then you also read how it's easier if you're also chaging valve cover gaskets - maybe I can wait till they start leaking! My wife's car still has factory plugs in it - only 65K miles. Should I wait till they start misfiring regularly?
I actually don't know how many miles they had on them...that's why I changed them. I didn't think I would do them until spring, but we had a warm day and I had the entire day free, so I took advantage of it.

The car has 110K on it, but I don't know if/when they were changed. They didn't look too horrible and I haven't really noticed a difference in power (don't know about MPG yet) but at least I'm good for 60K (3 years or so) now.

I used the same as stock. NGK platinums. They're supposed to go 60k according to Subaru, but realistically they probably would last longer than that without any issues. No matter what you do, stick with NGK, but you could use iridiums instead if you wanted since they'll go 90k. I went with the platinums because advance had everything 20% off this weekend and didn't carry iridiums.
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Actually, I'm ashamed to say I already have the NGK Iridiums and, uh, they've been hanging around for quite a while. I got them when her car was throwing misfire codes - ended up being a bad battery. Only 65k but almost 10 years. maybe I'll tackle that job in April. I've never changed plugs in a DOHC car of any type and also have no experience with coil-on-plug.

The coils are nothing difficult. The only automotive plug changes I've done have been on distributorless engines. Just a little pulling and such to free them from the plug (and that's only because of the space and angle you're given to work with on a Boxer), but nothing bad at all.

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?

Also helpful in tight spots is to take an extension and grind the male end a bit so it allows some wobble, you can get about 5 degrees of mis-alignment. These are sold as wobble-extensions, and are quite handy. They also don't bind like a full universal can.

They say your time is worth $100 an hour, so this one comes out about equal with having the dealer do it. Now I just need to find someone that wants to hire me for 3 hrs on a saturday!

That's what I've always done as far as tightening the plugs (about 3/4 turn past). Never stripped anything and they work perfectly fine.
do you have to tie them up outta the way ?

is there a procedure with pics somewhere?
Nope, they unplug so they remove completely and you just set them aside. Basically you take one bolt out of the side of the coil (12 mm), unplug it, and pull it off the plug and out. Nothing hard at all.

I think there's pics over on Scoobymods somewhere, but as mentioned there isn't much room to take pictures so I'm not sure how many/how detailed they are.
I didn't have any trouble at all...even got a torque wrench on them :)
That takes all the fun out of it. :D

Believe me, though...if I had to pull the engine for some reason I would be doing the plugs while it was out no matter how few miles they had on them.
I had actually replaced them a year ago when the engine was in the car. This is just me re-installing them after the rebuild.
It is interesting to see what I was working on, since with part of the frame in the way you really can't see a whole lot.

I'm good until 170k now...since I drive around 20k miles a year I expect I'll be at it again in late 2014.
Very cool album...looks like that project took some time!
I replaced my plugs from the bottom today and it wasn't too bad. The drivers side closest to the fire wall was the worst. Found that I had to unplug the coil pack on the drivers side closest to the fire wall to get the coil pack all the way out.

I would never try them from the top as from the bottom they are right there like JP said.

The engine does run a little smoother now.
...and sometimes just unplugging the coil pack is a challenge!

I think trying to get to the plugs from the top is an act of masochism. When I look at it from either side, there's no question in my mind that it's infinitely easier to do it from under the car. Glad someone agrees!

And we're most definitely on the same page as far as the driver's side firewall plug goes too. I think somewhere between 1/3 and 1/2 of that job was spent on the one plug for me. The others were relatively quick.

I didn't notice any power/running/MPG difference on mine unfortunately, but that tells me that the previous owner must have changed them at one point (or that they're really great plugs), and it gives me the piece of mind that they're taken care of for a while.
Did you have to rotate the boots to remove them?
Are you referring to the boot that contacts the plug from the coil pack? If so, I just pulled them off without rotating, though I'm sure it's possible that a little rotation could help.
Indeed, but I had watched some youtube videos of people doing the plugs on the H4. Totally different setup!
They sure are! The H6 is coil-on-plug while the H4 is not. Plus, it is much easier to access the plugs on the H4. I can get to both sides very easily from the top as long as I move some of the air intake stuff and the washer fluid reservoir out of the way. Definitely not the case with the H6!
Changed the plugs on my V6 Tacoma yesterday. Really puts into perspective how much more difficult the H6 is. Tacoma took me ~45 minutes, maybe less. My record on the Subaru was about 2 hours. First time was about 3.
When did the Gen3 die??? I missed it, what happened?
This, unfortunately:
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