By Justin Stobb on March 27th, 2012
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.
Justin
Your Independent Subaru Expert
Love the blog posts!
Great video
What a nice comment from a beautiful lady.
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
That Doesn’t sound like piston slap.
I would look into the Exhaust Heat shields.
Justin
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!
Cheers.
Thanks Ajay!!
No one is talking about the H3.0. I love the car, a little under powered for the size, but a realy nice car.
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.
You bet glad I could help!
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 !!
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.
Justin
By the way i have a 2002 subaru impreza 2.5 TS
You can also install Dyna Mat, I have provided a link here http://www.amazon.com/gp/product/B00020CB2S/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00020CB2S&linkCode=as2&tag=alwhdrau-20
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.
Justin
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!
I forgot to mention, ’00 OBW, 114K, 2.5
Thanks!
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
Justin
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
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.
Justin
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
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.
Justin
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!
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
I wouldn’t try to use 10w50 to quiet piston slap.
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!!!!
I like Castrol 5w30 synthetic blend for the 2000 RS.
Thanks for the feedback
Justin
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.
Thanks
Hi Rod,
Im not a huge fan of 10w40 unless its to break in a Engine build.
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?
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.