By on November 26, 2012

TTAC Commentator theduke writes:

I bought a 2003 Subaru Legacy SE sedan a little while back for my girlfriend. It has the “Phase 2” EJ25 SOHC motor. Living in Michigan the AWD is nice, and it was a one owner car with documented service history and I got a good price. The car has 105,000 miles on it, and the previous owner had the head gaskets and timing belts replaced about 10k miles ago by the Subaru dealer.

I have no complaints other than the car really ticks on cold start, and does so until it warms up when it the sound goes away. The car doesn’t seem to burn any oil. Based on what I’ve seen online (youtube video and forums) this vintage Subaru is notorious for piston slap and its supposedly nothing to worry about, although Subaru apparently will replace the two noisy pistons for persistent customers. At this point the car was cheap and runs well and I have no desire to tear it down just to replace pistons, but want to know its reliable for my girlfriend. So what are your thoughts on Subaru piston slap: ticking boxer bomb, or nature of the flat-four beast?

Sajeev answers:

Your letter reminds me why I have a love-hate relationship with Subies.  Some are quirky, illegally fun, loyal friends while others, uh, eat head gaskets, have piston slap and make the underhood’s labor intensive real estate borderline unbearable. There’s a reason why Toyota owns Subaru and not the other way around.

But let’s be clear on one thing: piston slap is just a terrible annoyance, not a serious concern for any automobile owner. It’s much like the TTAC column of the same name, son.

Now this website does a fair job assessing the situation. Piston slap is an unfortunate by-product of a manufacturer that picked the wrong piston rings for a particular motor. Your reseach is valid, you have very little to worry about.  It will suck on re-sale, if you sell it on your own to an unsympathetic buying public on craigslist.  But keep up with the maintenance, don’t thrash it and I predict it will last for another 50-100,000 miles.  If that’s what you really want.

Send your queries to [email protected] Spare no details and ask for a speedy resolution if you’re in a hurry.

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17 Comments on “Piston Slap: Subaru Piston Slap!...”

  • avatar

    Speaking of Toyota, a friend bought a used 04 Matrix a few years back and that thing had the worst piston slap I have EVER heard. It would simmer down as it warmed up but never caused serious problems. Still going strong at 130k plus. I know that GM had this issue with their fours back in the late 90’s as well.

  • avatar

    34 years as a Subaru tech.
    Many of those with alleged piston slap in those years had the problem turn out to be a faulty timing belt tensioner. If you have access to a mechanic’s stethescope listen to the area just adjacent to the water pump. This was primarily on the twin-cam engines.
    There were also problems with #3 rod bearings. Run the engine till hot, then repeatedly accelerate in neutral from idle to 3K rpm and see if the noise appears.

  • avatar

    My wife’s 2005 Outback has 156,000 miles. A couple of years ago, it started to slap on warm-up. After we replaced the water pump and timing belt around 95,000 (head gaskets, too!), the slap went away. Now it is coming back, but only at cold starts.

    I am thinking Terry might be right (above). I am also thinking I wouldn’t worry about it, and I plan to run ours a chunk longer. It really is only noticeable on a cold start in winter here in Maine. Drive it gently while it warms, and it should be fine.

  • avatar
    Angus McClure

    I think that half the cars I have owned sounded like that.

  • avatar


    You mentioned: “Piston slap is an unfortunate by-product of a manufacturer that picked the wrong piston rings for a particular motor.”

    Correct me if I am wrong. Didn’t you mean that piston-slap was causes by an undersized piston? (If the rings were undersized, the engine would burn oil and you would notice that.) What causes the “slapping” sound is that the skirts have more play than they should and hit a bit harder (and harmlessly) on the lower cylinder wall.


    • 0 avatar

      Honestly, I do not know. The rings and the pistons both play an important part. See below:

      “In the case of the famous GM piston slap engine defect, the piston design with hypereutectic (high silicon content aluminum alloy) pistons, reduced or eliminated piston skirts (to reduce reciprocating mass), and a higher ring pack to reduce unburned fuel mixture on the sides of the piston crown have made piston to cylinder bore fit much more critical.”

  • avatar

    My MR2 has wicked piston slap as well, my mechanic tells me its nothing to worry about, just keep checking the oil and doing changes regularly. If the engine ever dies I will probably swap in a 2ZZ anyways.

  • avatar

    I had a rattle in my ’09 2.5 Legacy. A mechanic at a dealer said that it was a loose heat shield. It turned out that bottom end ate itself. Keep checking the oil.

  • avatar

    Our 1998 with the 2.5 twin cam engine has always made this noise until it warms up. It has 230k miles on it. Engine repairs have been two timing belts and, seven years ago, the head gaskets. It does burn (not leak) enough oil that I check it every thousand miles and have to add a couple of quarts between oil changes at 3,750 miles intervals. The Check Engine light comes on occasionally and the codes are either a misfire or catalyst efficiency. I just clear them and keep driving.

    If you keep up with routine maintenance, especially oil changes, your girl friend’s car should last a long time. Note that mine is a 5-speed manual. I don’t know how long the automatics last.

  • avatar

    It won’t suck on resale. Just warm up the car before the potential buyers come by for a test drive.

    This is yet another reason why you have to insist on a cold-start when you are shopping for a used car.

  • avatar

    I just watched the video and heard the noise. Because it goes away once warm, and assuming it’s not a tensioner going out, as another poster suggested, I would not worry about it. Noisy engines when cold are pretty common.

    A noisy engine when hot is another story.

    Aside from just driving the Subie and enjoying it (I love Subaru seats, and the simple, legible gauges in your car make me smile)you may want to double check the oil you are using. I don’t know how hands-on you are with your car’s maintenance, but you could experiment with different viscosities to see if one works better than another. I’m a big fan of Rotella Synthetic (yes, it’s a diesel oil, but it’s a great oil for most applications).

    I would not go with an engine flush or any BS oil additive. But good oil, is good oil.

    Good luck with it. As others have posted, with proper maintenance, I think this car will last you a long time.

  • avatar

    The GM Pistons referenced had SHORT SKIRTS, the sides of the pistons below the rings. Piston Slap IS the Piston Skirt tapping against the Cylinder. It is caused by skirt wear and sometimes a bad or binding Wrist Pin. Neglecting oil changes is the easiest way to get piston slap. Boxer engine pistons wear more at the bottom due to Gravity. GM engineers are not the best and GM just doesn’t care what happens after the Warranty runs out. You can use Motor Honey to quiet it down.

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