Too much oil = piston slap?
Hello all - I have a 2004 Forester with 51K miles. About 5 months ago I was changing the oil in my car which I have done about half the time since I bought it 5 years ago. I accidentally drained the AT fluid, but then filled the oil up with 4 quarts. So the engine had 4 extra quarts in it. Don't know what I was thinking (obviously I wasn't). I started it up and didn't notice anything wrong, but as I pulled around the block I noticed the smoke coming out the exhaust pipe and some slipping in the transmission. I turned around right away and only traveled less than a mile. I immediately realized what I had done, so I drained the oil completely and refilled to the proper level, and I filled the AT back to the right level as well. After I ran it for a couple of miles the smoke went away and everything seemed to be fine.
A few months later I noticed that the engine was louder and it has a slight knocking or slapping sound upon start up, but it usually goes away after the car is warm (15 min). I took the car to the dealer and they told me it is a piston problem and would cost $2800 to fix. My warranty ran out in March of this year (based on years not miles). The mechanic did say that it should be repaired soon, but per many forums it sounds like piston slap is common in Subarus. I also have noticed that the car does not have the acceleration that it used to.
I have two questions for the forum:
1) Could the piston slap have been cause by my blunder of putting too much oil in the engine? I called around to several dealers and they have all said probably not.
2) Should I do something about the piston noise, i.e. try to get the dealer to honor the warranty since I am only at 51K miles? Should I bring it in for an early 60K standard tune up?
Any advice would be greatly appreciated. KH