Piston Slap - What year was problem solved or was it?

My '99 will do that occasionally if I don't drive it every day. I think the oil filter check valve doesn't seat and the oil drains out of the valve buckets. It only lasts for a second or 2, right? I think piston slap usually lasts at least until warmup.

I have an '02 OBS and it started doing something around 8000km. Not sure if it is piston slap, but it makes a knocking sound at cold start in the winter and goes away after about 5 min. Took it to the dealer last winter and, wouldn't you know, the car would not make the sound when it was there. They said I would have to leave it overnight which I couldn't do. I will reassess the severity of the noise this winter and decide if I'm going to push the issue or not.

If this is piston slap, I can't believe they haven't resolved the issue after all these years of knowing about it. This problem could kill Subaru if they keep ignoring it and word spreads.

Personally, I would never buy a used car that knocked on startup. Maybe this has not been a big issue because Subaru owners tend to keep their cars forever and never end up on the used car market?? Do we take the bad to get all the good?? I dunno.

Steve.

Anyone care to explain what piston slap is to me? Im pretty well up on mechanical stuff but never heard of this before???

Ross

This is very good link that explains what is "piston slap".

Ross wrote:

I don't know if they've addressed it since, but my 2000 OB received a brand new short block at just over 50K miles because of piston slap. Thankfully, it was covered under warranty.

-Scott

I had a case of piston slap in my 1949 Ford back in 1953. Pistons had been knurled to reduce oil consumption and the knurling wore off rapidly causing one piston to rattle. There ain't nothing to prevent a piston from rattling if the skirts are short or not up to diameter specs. It's a simple lever arm, the ratio of the distance from the wrist pin to the top of the piston where the detonation takes place off center compared to the distance to the bottom of the piston.

Same here on our 1998 @ 50K miles under warrantee. Our 2003 OB started doing it early on, 3K miles. It's the same ole malady, slaps when cold, OK after a warm up. The 1998 OK seldom got OK.

D>

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Actually, while it still exists, it's not as common as it once was. The slap, that is, not the actual problem that causes the slap. Bores that have worn oval cause pistons to fit sloppily. In the days of cast iron pistons the sloppy fit of the pistons in these circumstances would result in a distinct slapping sound at certain RPM. Of course, this would be accompanied by all of the other problems resulting from loose pistons. Modern pistons are not prone to the noise, but the other problems are just as prevalent as in the old days.

-- GW