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2002 Subaru Outback H6 3.0 Spark plug installation

Hi! Dne’ here once again! I believe that if a person is willing and able, then we should tackle maintenance on our vehicles vs taking to a dealer or local garage. It does require some common sense when taking “things” apart, and being able to put it back together again, and of course a variety of tools! Like any good mechanic, I have a vast variety of tools! I love tools! ; )

Note: I performed this maintenance procedure a few years ago, but had the pictures on file and decided to put this on Classic Cars and Tools.

Here, our ’02 Subaru Outback with the 3.0 flat 6 cylinder was getting close to 95k miles, and really nothing had been done to the engine about spark plug replacement and O2 sensors, and fuel filter. But the Outback also did have an oil leak coming from both valve covers! do I really want to attempt this! yeah!

I love the look of this engine, and the engine cover! Especially after washing it and applying a little Armorall! First mention in taking the engine cover off~ visibly there are I believe several 10m bolts on the top, but after removal of these, pull the engine cover forwardly, then up, then it can be lifted up and out easily. On ours some goofball didn’t pull it forward and broke the front retainer clips! argh

Henceforth, I will not be going in order of a step by step process. I didn’t document every detail, but the most important is mainly how to gain access to the plugs; )

The quest here is how do I get these spark plugs out! Much less the valve covers!? One has to remove the coil packs which are over each spark plug! The coil here is recessed low and difficult to get to! hmmmm

First, one has to jack up the car and put some jack stands for safety!  Here I bought a new plastic thing that goes beneath the engine. Ours was destroyed by oil changing places and general wear. The new one looked very nice and was only about 80 bucks from the dealer. Notice I didn’t say 79.95.  I despise everything these days are like, 19.95, or a car for 29,995.! give me a break!

Note: there is a sound deadening material on the other side(not shown). Maybe you can see part of it that has come loose in the old cover. That material gets very nasty especially if your engine has an oil leak. This old oil gets heated up by the exhaust and engine heat and can smell, the smell can make its way to the engine cabin~ then you may get a whiff of burning oil from time to time. Fire hazard? Who knows! Check your valve cover gaskets!

Once the car is up on jack stands and the lower engine cover is removed. You have to disconnect the exhaust from the exhaust manifolds. There are only six nuts and maybe an exhaust hanger back a ways. Just let it gently hang down.  Then there are two nuts that need to be removed that secure the engine or motor supports. Now one side at a time, the engine may be raised. Here I used a bottle jack placed on a few blocks to elevate the bottle jack. You must find a solid place to jack the engine from, then SLOWLY raise one side of the engine, I said one side at a time! ; ) This will raise the engine and the spark plugs to where they can be more easily accessed. More easily, not necessarily easy ; )  Now don’t go crazy thinking you can raise the engine higher than necessary~ there are hoses and other things connected to the engine as well. Just go slowly and only as high as needed.

Note: the nuts that hold the engine supports are a shallow nut, and your socket can easily slip off. Use a good tight fitting socket. I used my air impact and came off fairly easily, but if you’re using a wrench, might be a little testy! ; )


Take a close look at this picture below! Notice all the oil residue on the frame and crossmember~ That’s from the leaking  valve covers~ugh~ makes my skin crawl that this poor engine has been so neglected! : (  but I have the technology, I can make this better! ; )


Important Note: Though it may not be absolutely necessary to drop the exhaust, I must have deemed it necessary, otherwise I wouldn’t have dropped it (disconnected it from the exhaust manifolds). But while going back over my blog last night, and you should decide to do as I did and drop the exhaust, please put a baggy over the exhaust or stuff a rag in it~ so there won’t be a chance of dropping a nut or bolt down it! Gives me nightmares! ; )

Not mentioned, but there are things that need to be removed to have good access to the valve covers and plugs. Just take pictures and use baggies to store your nuts and bolts so you won’t lose them!

The spark plugs are actually easier to remove if replacing the valve cover gaskets! there are several 10 mm bolts that hold the valve cover in place, then the valve cover may be removed and cleaned up in preparation for new gaskets/o-rings gaskets. The coil packs are each held in place by a 12 mm bolt. Unbolt it and the coil pack can be unplugged from the plug and moved out-of-the-way. Be sure to put the coil pack on the same plug you took it from! Doah!  The picture below is the passenger side of the engine.

Important! When re-installing the coil packs on to the spark plugs, put some Dielectric or connection grease on the part of the spark plug where the coil pack plugs on to. Just a little dob. Little packets may be purchased at the counter at auto parts stores, you don’t need a great big tube of it!

With the valve cover removed, the spark plugs are staring you in the face and easily accessible with the correct sized spark plug socket(with a protector inside so not to damage the ceramic part of the plug). Remove the plugs and install your new plugs now, be sure to check the gap before installation. You don’t want to have to pull the plugs back out for another 80 k miles, right?

Important: When installing the new Spark plugs, don’t forget the Dielectric(mentioned later or earlier), but also place some anti-seize compound on the threads of the spark plugs! Don’t get crazy with the stuff and don’t get it on the electrode tip of the plug! You do want the spark plugs to be able to be removed again some day, right!? ; )

Here on the driver’s side, the battery and other un-boltable things need to be moved out-of-the-way to access the valve cover and plugs. You must remove the windshield washer tank and battery. One or two of the valve cover bolts were a little testy to get out,  be patient, they’ll come out.   Another part to replace while you’re at it is the fuel filter, right behind the windshield washer reservoir, plus the fuel filter will be easier to access with the reservoir out-of-the-way! : )

Also a great time to clean up where the battery sits! Please wear long sleeves on the side of the engine, the battery residue can mess with your skin, you may want to at least take a moist rag and clean this area before the task at hand.

Now my dear car DIY friend, if you’re not going to replace the valve cover gaskets, just replacing the spark plugs, then do so, but make sure the valve covers aren’t leaking!!

below: this is on the passenger side. Here one coil pack removed, you can just make out the hole where the spark plug lives, kind of like a Hobbit! lol  Got to have a little fun, right! Don’t think of this as a chore, it’s an accomplishment! You can do it! ; )

below: this is the driver’s side bottom of the valve cover. Notice the oil drops hanging from it! These little oil drops drip onto the exhaust pipe and smoke and smell! Replace the valve cover gaskets!  Now, this is another good time to replace something else, The O2 sensors! There are three of them, and they are quite expensive, but necessary! I just replaced the two up front. Notice the blue wire? which leads to the driver’s side O2 sensor. I won’t go into detail here in its removal, pretty much common sense to remove it if you’ve made it this far. Be sure to put some anti-seize compound on the threads.

This is the driver’s side. If you don’t replace the valve cover gaskets, at least the plugs are accessible now, and you have done well! ; )

below: This is a great time to clean up the valve cover and make it look new once again! I love clean parts!  Buy your new gaskets from a local Subaru dealer, I don’t believe your local auto parts have them. I do believe in factory parts despite the price. Just think how much money you’re saving by doing this job yourself! Personal satisfaction and knowledge attained! 😉  As far as putting sealant on the gaskets? I don’t believe it’s necessary. I did put some permatex thinking I was doing myself a favor, but the permatex smelled for a long time! These are machined surfaces, just put the valve cover back on like this and all should be well.

This is actually the finishing up of the job of replacing spark plugs and valve cover gaskets. The engine is clean once again and maintenance goal achieved. Be sure to write your own service order and the parts purchased and keep a record. If you don’t, amazingly you’ll get down the road many miles later and ask yourself, “When did I do all that work?” haha! Keep good records!

PS: if you should ever have a growling power steering when turning the steering wheel, it usually means it’s sucking in air, and usually happens at the pressure hose. The o-ring becomes old and allows air to be sucked into the system causing the noise! very irritating!

I hope this has helped, and thank you for coming to Classic cars and Tools! If this helped, would you please leave a nice comment, and maybe even subscribe! ; )

Your car enthusiast friend!  dne’  ; )

41 Responses so far.

  1. Dennis F. says:

    Hello Dne! Thanks for the beautifully clear walk through article on changing the Subie plugs & vc-gaskets! Those photos are excellent and your info clarified most if not all of the “mystery” on the gaskets. Given the dealer ‘labor charges’ of approximately $510 + parts + tax, I’m going ahead and changing these myself!

    I did have one question … why did you choose to change out the O2 sensors @ 95K … is this a factory recommendation or just something you felt was necessary at that mileage?

    Thanks again, your hard work (auto & computer/website) is a real gift!

    ~ Den

    • admin says:

      HI Dennis! I’m so glad it helped and I do appreciate your response as well! The spark plug/vc replacement on this Subaru gets more hits on my site than anything, but I never know if it actually helped anyone as no one says so. lol It’s definitely a chore, but doable! Thank you again! ; ) dne’

  2. angelo says:

    Thank you for the great info i was staring at my H6 subaru for over 10 minutes and thinking how on earth am i going to change the plugs ,they are so close to the body chassic now i know how bit its still not a easy job due to being very careful not to break the small wiring clips that plug in the coils ,no one has said ,but thanks anyway great help and diagram. and to subaru, why is it so hard from factory to have plugged holes through the body so us the humans can run a long socket ,so we do not have to lift the motor ,it sounds very stupid just to change the plugs,and let me tell you very bad motors for towing a boats they struggle tow tow and waist a hell of fuel when towing ,my other 2004 mitshubishi verada front wheel drive tows alot better and better on fuel thats for shore and yes it was a subaru 2006 h6 outback no good for towing very weak and firsty. good subaru cars drive good ,but no good for towing .no offence to all. they are just for looks

    • admin says:

      Hi! Angelo, I totally agree with you! I haven’t a clue why they would make changing spark plugs so difficult on these cars, perhaps another way the dealership and auto repair places can make money? Thankfully, they don’t have to be changed very often! However, when doing so, it’s a good time to clean up the engine compartment, tidy it up, plus learn what’s under the hood for future reference. Once you get all of the bolt on stuff out of the way(air cleaner box, battery box, etc), then it’s not terribly bad, but still a chore. I’m happy to say that we finally sold the car so I don’t have to deal with the thought of working on this beast anymore! But I must admit, this Subaru was a very dependable car! Thank you so much for making a comment! I love visitors on my site and glad that I was able to “lend a hand”!! 😉

  3. Very Kind of you to go to such trouble to create such a super article on the Subaru outback H6 , I bought mine at a very low price and it was in an absolutely filthy state inside and out . However , i have enjoyed cleaning up and servicing this car , and your photographs have been a wonderful help . now at 110,000 miles she is running real sweet ! Much appreciated .

    • admin says:

      Thank you Hugh! The H6 is a wonderful vehicle! However, many people out there in la la land don’t take care of their vehicles! 110k miles~ that’s just getting broken in! 😉 I’m glad to have helped!!! 😉

  4. Ben Page says:

    Thanks for making this walk-through! The Haynes manual has almost no mention of the H6 engine and there are very few places to get instruction for working on it. It would never have occurred to me to lift the engine up just a bit.

    • admin says:

      Thank you Ben! Thank you for the wonderful response! The H6 spark plug and valve cover gasket receive more hits than anything on my website! I’m glad I’m able to help the DIY folks! Luckily the plugs don’t have to be replaced very often!;) dne’

  5. Rogy says:

    This is an most excellent post. AS an old subie owner of the 4 cylinder variety, 13 from 1980-1999, the H6 i have lusted after, arrived. The fours were better performers than my 1959 VW, but wimpy (adequate) but one still planned freeway accessing. But having enjoyed the easy access, (engine, clutches, etc replacements), I find your H6 plug replace great. I do long for the older 15 min. plug replacement.
    I have two 2004 L.L. Bean.wagons. 187k and 146K. so plug time. no leaks happily. and my wife still wants to put in a six speed manual.
    Thank you for the post.

  6. Sue says:

    Thanks Dne for your helpful info! It’s the best I’ve seen so far! Do you have any other helpful DIY mechanical tips on 2002 Subaru outbacks? I’m looking at changing my cv joints as they’re clunking again

    • admin says:

      Hi Suzanne, and thank you for the compliment!;) I found a link on Youtube and looks to be pretty much self explanatory regarding the CV axle replacment. I’ve replaced CV axles in several other cars, seems the only difference is the roll pin holding the axle to the transfer case/differential. The replacement looks to be a relatively easy task. If the link doesn’t work, you might type in the question on Youtube. http://www.youtube.com/watch?v=jtZMwaCCMdU Just curious how of how many miles are on your CV axles now if they’re “clunking again”? They should last quite a while! dne’ 😉

    • admin says:

      Hi Susanne! Thank you for the great compliment, I do appreciate it;) As for replacing the CV axles, I found this youtube link http://www.youtube.com/watch?v=jtZMwaCCMdU How many miles are on the current axles? they should last a while unless you did put a lot of miles on the vehicle.;) dne’

  7. Sue says:

    Hi Dne, I’ve done 217000km (Australia, not America sorry

  8. Dan says:

    Thanks for the good detail. Just did this on my wife’s VDC H6 and now have to to my daughters car as well. One thing I noticed was the Left cover has the PCV valve screwed into a port to draw from the lower half of the cover. The port and PCV valve were both plugged. Wonder if this is what leads to gasket failure. Both my cars started leaking at about 100K miles. None of the service stuff I have says to change the PCV valve, but I’ll be doing it every 30K miles from now on.

    • admin says:

      Hi Dan! Thank you! On the pcv valve, or positive crankcase ventilation valve back in the 60’s and 70’s, they were notorious for clogging up mainly due to cruder oil or less efficient oil gumming them up and crappy gaskets. A clogged pcv will result in increased crankcase pressure and the pressure has to go somewhere to be released, usually resulting in valve cover leakage, or oil pan leakage. Tune ups always, or most always included a PVC valve, and it’s good that you took note to that and changed it out, it is easily neglected! Over time, the rubber gasket around the valve covers just give way to age and heat and become hard and brittle, then it’s just a matter of time before the first drip!:( You may want to run some Techron fuel additive to help prevent sludge build up(I buy it by the case at Oreilly’s auto parts). I run it in my Geo Tracker due to the EGR valve becomes easily gummed up with sludge and the Techron seems to help, and getting gas at Chevron as well since it contains Techron.
      Though we don’t own the H6 anymore, we do have an ’06 Subaru Baja turbo model which has 88,ooo miles. I haven’t even paid much attention to the plugs on it yet! lol

      Great job on your “Tune up”!! I always finish the job by using engine cleaner and making the engine compartment shine! I know my engines love to be pampered, nothing like a clean engine compartment!
      Thanks!!!! 😉 dne’

  9. Po says:

    I just replaced my oil cooler gasket and this is going to be my next project. I am wondering is there a gasket on the exhaust? If yes do I have to replace after dropping the exhaust?

    • admin says:

      Hi Po, I did not replace the exhaust gasket/s and had no leaks afterwards, but if I had it to do over again, for just a few bucks more~ go ahead and buy a new gasket/s; I do like factory gaskets vs. parts from the local auto parts. The amount of work which will go into replacing the spark plugs deserve factory parts, and if you decide to replace the valve cover gaskets, I definitely believe would buy factory parts. Have all your parts ready on the day of so you can focus on the job without having to worry about parts, however there are times when you come across other things that may need replacing while your at it:( Whenever you get around to the spark plug change/valve covers, let me know how you do!;) Thanks for visiting my site!! dne’;)

  10. Po says:

    Thanks for the excellent write up and answering my question, I will have everything ready when I start this. I went through some forums including your blog, nobody mention about drain the oil, is it too fundamental to mention or there is no oil in there when engine is not running?


    • admin says:

      Hi Po, there may be some residual oil in the valve covers, but nothing to be concerned about, a little dribble perhaps. Just take your time, take pictures, make notes, I even did mini videos before diving in! 😉 Let me know how you do!

      • Po-wen Wu says:

        Hi DNE,
        Finally I replaced the head cover gaskets and spark plugs last week. I worked on passenger side first without jacking up the engine. But on driver side, I had to jack up the engine a little bit to have access to the last head cover bolt(but still very hard). Thank you very much for your article, pictures and tips to help me went through this. You are right, the feeling of accomplishment is priceless.


        • admin says:

          Way to go Po! It’s no easy task for sure, but you got after it and did it! I’m so happy to have helped a little bit! You should be good to go for another 90,000 miles!
          dne 😉

  11. Joe Rogo says:

    Hi – thanks so much for detailing the plug job – not so scary now. I have a question for you:
    I’m considering an Outback H6, ’02, 153kmi, claimed to run well, but has an oil leak, minor. What do you think are the odds it’s valve cover gaskets (not too scary) vs head gasket failure (scary)? I’ve heard the H6 is reliable for head gaskets, but don’t know my odds here.

    • admin says:

      Hi Joe, thanks for the compliment, now onto your question~ odds are great that it’s just the valve covers. As you may have read, the lower cowl, the big plastic cover underneath the car has a fibrous material which also acts like a sponge, so it catches the oil, so not only does that reek of the smell of burnt oil, so does the drippings getting onto the exhaust. As with any Pre-owned vehicle, we take a chance on what the cars previous problems(if any) will present themselves. If you like the H6, which is a great car, and you have good mechanical skills, and the price is right, go for it. But use good logic in your buying it. You know at 153k miles on a ’02 is going to need some work! I’ve never heard anything about their head gaskets being a significant problem. However, the usual checks for oil in the coolant, or coolant in the crankcase, or it smokes steam out the tail pipe, well, those symptoms would be something to stay away from. Look forward to what decision you make.
      dne’ 😉

      • Joe Rogo says:

        I cannot believe how quickly you replied. I was just checking that my question got through. You obviously really love fixing stuff, which is what I reply when asked, “what to you do?”

        The Outback is asking $2400 and looks nice in pics, so not a huge risk, but a 160 mile trip one way to look. Ad said one mechanic called it minor/easy, another said could be head gasket. Maybe he/she’s not familiar w H6 & generalized on the H4 reputation?

        You’ve given me very pertinent questions to ask by phone here (cowl been pulled? how much oil need to add?, coolant stable? exhaust steam?[I know that one well]), so many, many thanks to you!

        BTW. I just passed on same car w/285kmi ($1300, just too rusty), but the test drive impressed me that an H6 engine w so many miles still ran like a Swiss watch!

        • admin says:

          Hey Joe~! Yes, I do love fixing things! kind of a “jane of all trades?” lol just out of curiosity, have you checked the Kelly blue book just to see what it may be going for? And you know, 2400 should translate into 1900 or 2000 if it’s what you want. You can use the problems with the car as factors which may reduce the price. Sad thing about cars today, they’re neglected big time! oil changes become less frequent, cabin filters never changed. one can look under a hood and see neglect of a dirty engine. Nothing like popping the hood and seeing a squeaky clean engine! I do agree that 160 miles is a journey! but I have driven long ways to buy what I want! Keep in touch, my husband is bugging me to go do something since its a nice day! Let me know what you find out! dne’;)

          • Joe Rogo says:

            Hey, I’m out looking at Subarus and found you again!

            Can u explain how to tell if an oil leak is coming from that oil cooler? I’m looking at ’01 w/112kmiles, but oil was low (1 1/2 qts) & oily mess under passenger side head. We’re on our way to mechanic now to pull cowl, but I don’t know if I could tell between head gasket and oil cooler leak.

            More about the other Outback later – it had oil IN the radiator. Possible crossover in that oil cooler? I could get that one for $1k..

  12. Perry says:

    Dne, thanks for the guide. It’s helping me enormously. I had a fair idea how to do the job but your guide have given me a few tips to make it easier. Cheers, Perry (Australia)

  13. Charles Sims says:

    Thanks. Was able to successfully do the covers and plugs. I did my passenger side first and having noted that others didn’t lift the motor, I did it without a raised engine. It was arduous but finally doable. I began the driver’s side and found it to be much easier until I got to the back lower 10mm cover bolt that is over the cross member support. I thought no engineer would be stupid enough to put one in a non-accessable location. I finally remembered your lift suggestion and found by lifting the engine perhaps 1.3 inch, I was able to see the bolt and get a small 1/4 drive ratchet on it. I had somehow managed to get the back coil off and up without the lift, but I found that I needed closer to a 2″ lift to get it back in and that also made it easier to get the little ratchet (with vice grip attached for extra length) to tighten the bolt back. Also, I needed to set that bolt on the cover with some tape before installation. Perhaps a two or more inch lift would have helped. It might be nice to emphasize how easy it is to unbolt the only two engine mounts (one bolt each thru the big cross member, and on my 13 yr old car they came off easy with a ratchet). Perhaps the long dripping oil kept them lubricated!
    Oh, you implied that dielectric grease should go on the plug contact. I believe it is only supposed to be on the upper part of boot and perhaps on the plug ceramic.

    • admin says:

      Thank you Charles for the great write-up! This will be seen by other viewers in an attempt to offer ideas to accomplish the job in question.
      dne’ 😉

  14. Sisinnio says:

    Thank you so much for this post. I could do the job just as you described it.

  15. Graham Burn says:

    Hi dne’ I have been putting this job off for too long but feel much more confident now having read your post, I bought the plugs a couple of months back then last month my wife suffered a breakdown when coming home from work so I think it’s time I gave it a go.
    Valve cover gaskets started to weep a few years back but was told it was an engine out job to fix, at least I know different now.

    • admin says:

      Hi Graham, welcome to my Classic cars and Tools blog! First off I pray your wife is back to herself! Life can be tough at times as it is one great big roller coaster ride! Now, that being said, just take your time, be safe with that engine being jacked up. It’s a testy job, but you’ll feel good about getting the job yourself! Let me know how you do, this will help others as well!
      dne’ 😉

  16. Graham Burn says:

    Thanks yes my wife is much better now! I’ll be sure to report on how the job goes and let everyone know how it goes.

    • Graham Burn says:

      After the snow and rain it finally was dry this morning so decided to get stuck in, battery and washer bottle out to access passenger side and air box off to access drivers side(rhd), managed to get all the coil packs out without too much trouble rear ones are a bit tight but if you turn them the right way they come out quite easily.
      Changed the front 2 plugs on the passenger side then thought as the covers are coming off it might be better to remove them first so started taking out the cover bolts, upper ones no trouble but the one at the back above the crossmember was a pig as it’s out of sight so could only get the spanner on by feel at least once cracked off it came easily with finger tips, I’ll need to get under to get to the other bolts, so far I haven’t lifted the engine, hopefully the cover will come out without lifting the engine?
      Rain stopped play today so hopefully I can get on some more tomorrow

      • admin says:

        Hi Graham! As for removing the cover without jacking the engine, I can’t answer that, but I can say if the covers can be removed, then access to the spark plugs is much much easier! I do know also that the plugs can be removed without jacking up the engine, but it’s just more tedious. Keep up the good work, let me know what you do! 😉

    • Graham Burn says:

      Managed to spend another couple of hours on the beast today, the cover did come out without jacking the engine and access to the back plug was much easier with the cover off which was just as well as it was tighter than the other 2 on that side for the first few turns.
      Cover is now back on, coils back on, just the pig bolt to finally nip up(the one in the back bottom corner) then can move on to the other side, I’ve taken the air box off in readiness and access looks similar tp the other side, tight! it’s at times like this I could do with smaller hands!
      Will keep the updates coming as I go.
      One thing I discovered was the hose from the PCV was perished and snapped when I tried to remove it so will need to check the others while I’m at it, the PCV was a bit dirty but didn’t seem to be blocked so gave it a good clean before I put it back.

    • Graham Burn says:

      All back together now, the drivers side went a lot better, I released the wiring from the oil pressure sensor and the injectors which allowed the harness to be moved out of the way, I also released the hose bracket from the suspension tower which made removal of the cover quite easy. With the cover off the plugs are easily changed, most of the time spent is removing items to allow access to the area of work then putting it all back again.
      Hopefully I’ve cured the oil leaks although I suspect I might have a leak from the timing chain cover, will give everything a good clean and then we’ll see.
      Anyway all done without jacking the engine and mostly from above, I only needed to get under for the bottom bolts on the covers and the oil pressure lead, so all in all not too bad except for the pig bolt on the left hand cover!
      Hope this helps others and thanks for giving me the confidence to have a go!

      • admin says:

        Way to go Graham! You should be good to go for another 80k miles~! your story will be on the tail end of my blog~ it’s good to have different approaches, then the DIY’er can make their choice, and who knows, someone may yet come up with even a shorter/quicker way yet! thank you for sharing! and have a great new year!
        dne’ 😉

    • Graham Burn says:

      As a proffessional marine engineer the engines I’m used to working on are somewhat larger but I’ll have a go at anything! Unfortunately this is not the end of my journey as I’m hunting down a misfire which has prevented me from driving my lovely car for several weeks now.
      All the best for 2018 from a wet and wild Wales!

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