All Wheel Drive Auto: Independent Seattle Subaru Service


Subaru Piston Slap


If you have owned a Subaru for any length of time you may have heard the term “Piston Slap”.

In the video below I try to demonstrate what piston slap is and what causes it as well as the compression rings and oil control rings on a Subaru piston.   I want to stress that piston slap can be inherent in many other makes and models but because Subaru does not do too much in the area of sound deadening it can be more obvious in a Subaru than another make.

I also want to point out that in most cases piston slap poses no detrimental effect on the longevity of the engine and instead is just more of a nuisance than a concern.

Thanks for reading and watching.


Your Independent Subaru Expert


51 Responses

  1. Hey Justin,

    Thanks a lot for your videos, they are amazing :-). Quick thing, I just stopped at your piston slap video and the page is blank, could it be a broken link or something?; do you have a link where I could see that video?


  2. Hi Justin,
    From reading all the previous conversations i am aware that this query will be slightly repetitive. I have a 2005 1.6 petrol Subaru Impreza 4wd with 112k on the clock. For the past 6 months the loud rattling under the engine has been getting worse. As most of the comments have outlined it’s loudest when cold but now it’s occuring most of the time during drive especially when accelerating. Another problem is that there is considerable lag when i am accelerating.
    It’s not drinking oil but i am filing it more often. I brought it to a few mechanics and they sent me away. One mechanic this evening to change the engine. I intend on driving it from Ireland into Europe in a few weeks as i am working in belguim for a year.
    What’ll i do, should i sell it, change the engine or risk being abroad on my own ( with considerable lack of knowledge) and it breaks down?

    thanks for any advice.


    1. Hello Joan,

      Its just tough to say without hearing it my self to know if it’s the engine or just exhaust heat shields?

      The lag and the noise may be unrelated as well.

      Your going to have to find someone there that can help, the car has a lot of life left in it, but it sounds like there are some repairs looming, if they are done correctly you should be just fine, but I do get the concerns, thats a tough situation that I just cant help with from so far away.

      There has to be a good Subaru shop there somewhere, research is really all you can do right now.


  3. Justin Hi,

    I enjoyed your video on Piston Slap. I am concerned because I have a 2015 Outback and have experienced this clatter from day one at cold start up. The performance is fine and I don’t burn any oil. I now have 3000 miles and just had the first oil change. I was told that because the outback uses a break-in oil the noise would subside after the first change. Didn’t happen. I also have a 2015 Forester and the problem is non existent. It only has 1000 miles on it. It runs and performs much smoother than the outback. I noticed a slight clatter under load starting at the bottom of a hill etc. with the outback. Any suggestions.

    BillW from Connecticut.

    1. Hi Bill,

      If the noise you hear is piston slap, it posses no long term detriment to the engine. If its something else it needs to be investigated, did you ask the service department if the noise you are hearing is in fact piston slap?


      1. Justin Hi,

        No, I have not. I have been reluctant. My observation has been that this dealer is good at oil changes but only has a few well trained technical people for the hard stuff. I could be wrong. I hope so. I will make an appointment and let them know what the problem is. I will let you know the outcome. Thanks again.


  4. Have not seen mention of increasing the octane in fuel to slow the flame front. Would a ‘slower’ burn affect slap?

  5. Hello Justin, nice explanatory video about piston slap. I have a similar problem with my 02 WRX. Recently I rebuild my engine, New NPR pistons, new oil pump, new timing belt kit, etc. Quickly after the rebuild I started noticing the dreaded noise and it has become progressively louder, even when the engine is fully warmed up you can listen to it (it’s louder when the engine is cold and it calms down as it warms). This is a video I made and I would appreciate your opinion.

    Thank you.

    1. Hello Josue,

      Do you know what the rings were cut too? Are the pistons over sized or STD? It’s always hard to tell on the videos, but it sounds like forged piston slap to me, there seems to be another noise however that could be a cam belt guide set to tight, I would look into that..


  6. Well this is embarrassing, but I ran my Outback out of oil (heard the rattle when I took my out of it to slow down on the Interstate) now there is a horrible knocking and have been told 3 things: rod knock=new engine or $4.6K, piston knock=new engine for $3.2K, and piston slap=new pistons for about $2K…any suggestions on what the best choice is? Just rolled over 100,500 miles, 2006 Outback 4 cylinder and has been well maintained…till now!
    Thank you

    1. Hello Cathy,

      Sorry to hear about that, but life does happen, and lessons are generally pricey.

      I am confused as to what you are being told, as either way the cost to replace the engine should be the same regardless if it’s a rod or piston failure. Piston slap shouldn’t even be part of the conversation.

      So I would opt for plan A and be more diligent on maintenance going forward.

      Hope that helps


  7. Hi. I have a problem hopefully you can advise on, I have a 91 legacy with boxer motor.
    A couple days ago steering wheel was going crazy left right while driving then a knocking noise started and is present every time I drive now. Steering problem disappeared but every time I put the car under load, driving not sitting there with foot on gas. It has a violent knocking noise. Just wanted your opinion as to what this could be and fixes for it, pref cheap.

  8. Hi Justin I have an 03 outback love the car but looking for a second opinion I’ve followed your site for a while now and Uve given very good advice but the slap in my car has gone a little extreme to me before I’d hear the noise n forget about it but the past few months its been getting extremely loud like it wants to go through the block is this because of the cold or major issue BTW I live in new York usually around 15 degrees I’ve heard that could be the issue and also have had replacing the pistons suggested

    1. Hello Justin,

      Its hard to advise on noise that I cant hear, it could still be an acceptable amount of piston slap or it could be something else entirely.

      It would be better to have someone look at it locally to you.


  9. Thanks for the informative and easy to understand video. My 2000 legacy has 252,000 and has cold piston slap. I just baby it until it warms up. I guess it will get louder and louder, but it’s not as bad as some I have heard. Glad to know it’s not fatal.

  10. Hi Justin, Thanks for your vid and explaining why piston slap happens. I realize you’re getting a few of these posts with people asking you how to get rid of the piston slap in their cars and i’d really appreciate any advice you can give me.

    I just did an engine rebuild on my 2.5L STi and have put in a set of CP pistons. They tend to loudly slap a bit on cold starts (which i was expecting) however you can still hear it slap around when the car is fully warmed up and has been driven around for a while. The car is still being run in on run in oil and i’m wondering if the excessive piston slap will cause any damage especially since it still slaps when the engine is warmed up.


    1. Hello Mena,

      CP pistons will make noise forever. They have a centered wristpin rather than 8 to 10mm offset, nosiest pistons you could have ran I am afraid but they do work well in their intended purpose..

      Generally speaking this presents no problem, but I also want you to understand that performance and longevity do not go hand and hand. Performance builds will never last as long as a factory short block, just hold up better to power enhancements.

      Hope that helps


  11. I should have mentioned that based on your explanation I would not have worried about a little slap noise but they had gone ahead and done this before putting the car up for sale.

  12. Hi Justin. Great explanation. I am buying a used 2000 Forester for my dad and the shop that is selling the car replaced the pistons to remove the slap noise. No noise at all on cold startup that I could tell. Very nice and tight car so I am going ahead wth it.

    I have a 2005 Legacy GT with 150k miles. I’ve never had piston slap on this car. Did Subaru change something to remove the likelihood of this noise?

  13. Just great video, this coming from a long time suby lover.

    I am picking up a 2000 2.5rs impreza 4dr with 94K miles on it. The good thing, the gentlemen selling it is a mechanic at a subaru dealership. He replaced the head gaskets, timing belt, and other items during his ownership, about 1 year. I gave him a few extra bucks to do the diff and tranny fluids including the plugs.

    The car does have piston slap, which I noticed while test driving it.

    I have been doing some research and I keep reading about rotella 5w40 oil. I also know that oil really does not to quite down piston slap. Is this rotella oil something worth using or just stick with a good quality oil and oil fliter. I have a ’13 impreza as Sandy at my 07 subaru impreza wagon. I normally use puralator pure one oil filters.

    Also, on a side note, once I get the car, should I change to a high mileage oil life max life or stick with a good conventional 5w30 like penzoil or castrol, etc.

    Thanks for the help!!!!

      1. Justin, thank you for replying.

        So I got the car, all seems good and dandy. The gentlemen advised he was using castrol 10w-40 in the car. Am I right in assuming that this is not the best weight oil for this car regardless of piston slap.

        The oil is due for changing in a week or so.

        I assume there is no harm in going back down to the 5w-30 or even 10w-30?

        Please advise thoughts and comments.


  14. Hi Justin I use fully synthetic oil 5w40 in my 2.0 turbo impreza wrx. its about 300hp. Its got piston slap when cold, do you think going over to 10w50 oil might help ??? Thanks Stuart

  15. Justin – excellent video. It put me at ease after spending $2K+ to have my EJ25 long block rebuilt, and starting it up to the clatter! I was told it was piston slap, then I found your website and understand why Subies have this.

    Keep up the good work!

  16. Hi Justin, nice informative video you have.
    How can i fix the engine slap?
    Can i change the piston rings?
    Or both the piston and the rings?
    Also does it wear out the cylinder walls?
    Sorry for so many questions. Better be safe then sorry lol.
    2003 Legacy 2.5gt

    1. Hi Joel,

      You can spend $ redoing the whole thing and still have piston slap.

      Unless upon tear down its obvious there is something worn its better to live with the noise.

      But yes rings, pistons and cylinder wear all contribute to piston slap.


  17. hi justin nice video

    I just have a question and I hope you can help me I have 03 STI running 325hp and it has exactly that piston slap when its cold when car gets warm it is fine. But I wanna give the car a more hp. If I do that must I worry about the engine or does the slap plays no role ? just wanna bigger turbo and looking for 370 and I dont know if its matther that I have this little piston slap

    regads martin

    1. Hello Martin,

      Are you trying to make 370 wheel horsepower? Also I would not become fixated on a number.

      You are asking for disaster if you intend to increase the size of the turbo without changing the pistons to a JE or Weisco Forged Piston., which by the way are very noisy.

      It may work for a while but it will just be a matter of time before you break a ring-land and perhaps the entire engine.

      A Cobb Access port running a stage 2 map with the rest of the components to go along with it, is as far as you should take a stock STI Lower end.


  18. Thanks for the great info on slap – it really is worrying when you’re a first time Subaru owner and you’re experiencing this for the first time.

    Have a question, too – while I used to only hear the slap in very cold weather (and it went away after very short time), I’ve started to hear it until the temperature reaches around 115 degrees(monitored via a ScanGauge). This higher temperature slap isn’t noticeable at idle inside the car like the cold temp slap was, but gets very loud under load when first starting out – typically between 1,000 and 2,500 RPM. Is louder slapping under heavy load normal, and is this higher temp slap just a progression of symptoms in this case?

    3 months ago I had my head gaskets, TB, and a few idlers replaced by a Subaru dealer, and I’ve only really noticed the sound increase after that service if that makes any special difference. The dealer that did that change uses Castrol GTX if that also matters…

    Thanks for any feedback!

    1. Hi Brian,

      There are a couple of things that can bring about a increased awareness of Piston Slap after a repair. One is that the Burn in the cylinder is better “bigger” as a result of the newly resealed combustion chamber, if the heads were machined this will also decrease the volume in the chamber a bit as well intensifying the noise. So its quite possible that the noise is in fact more pronounced now.

      Next is the very real possibility of a heightened sensitivity to our vehicle after we have spent a large amount of $ on it. Its our nature to be reactive, its completely understandable i that’s the case. So its quite possible the noise is the same, or slightly loader, but after “getting out your wallet” you are more in tune to the vehicle, which can be a good thing.

      I don’t know which statement you and the Subaru fall into, I suspect however its a little bit of both, I would continue to monitor the noise and also check your oil every other tank of fuel just to make sure you get good value out of the money you already spent.

      Hope that helps


    1. You can also install Dyna Mat, I have provided a link here

      You can add this sound deadening material and it will make the Impreza much quieter. The reason Piston slap is less prevalent in other models from the drivers seat is the amount of sound proofing the Cabin has had from the factory, Subaru does not spend much $ on this for the Impreza at all.


  19. Hey Justin,

    Is there anything to do to solve the problem of piston slap.

    I find it very annoying and I’ve been told the only thing I can do is change the engine.

    Is that true ?

    thank you !!

    1. Get a better car stereo.

      Many modern cars have piston slap, I just rode in a 2012 CRV that had just as bad as any Subaru I have encountered.

      There is no reason to replace a good engine for a normal noise.


  20. Justin, Excellent instruction! I was trying to figure out the cause of my piston slap in a 2001 Saab 9-5. My oil control rings are stuck in the pistons thus three of four are scored. The previous owner and mechanic(s) were hacks. Thanks man.

  21. No one is talking about the H3.0. I love the car, a little under powered for the size, but a realy nice car.

  22. Justin,

    Thanks for sharing all these great videos you make. I find them so informative. You are truly generous with your knowledge, and that’s much appreciated. I feel so lucky to have AWD in the neighborhood. You guys rock!


  23. Hi Justin,

    Nice video on piston slap. I was thinking of you due to noise I am experiencing on ’08 Outback. The car was in an accident but put together back together very well. Nonetheless, it cost $13,000 plus when all was tallied. The noise I am experiencing is something over and above the low rumbling of the engine. It’s only occasionally, and usually on acceleration. It seems like a vibrating sound coming from directly below the front sears. It’s not really a rattling sound but of something attached well enough to take most vibration but that only occasionally vibrates. My mechanic has already said ‘that’s the sound of subaru’ in other words – normal. But I don’t think I had it before the accident. Any ideas of what it might be that I can suggest to my mechanic?

    – Kevin O’Connor

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