Piston Slap: Subaru Piston Slap!
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 sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry.
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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.
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.