Subaru piston slap


#1

My 2002 Outback with 125,000 miles has a noise from a cold start that sounds like old-fashioned valve chatter(a engine speed-related “tick-tick-tick”). The noise goes away when the engine is warmed up. My local Subaru dealer’s service department suggested that my oil had been low, but their oil change did nothing to fix the noise. On-line research suggests that the problem may well be the notorious Subaru Piston Slap syndrome. Questions:

1. Will Piston slap eventually devour my engine? (It’s getting worse, progressively. Onset was at below freezing temperatures only. It’s now apparent at 55 degrees (F).)

2. Is there anything I can do to slow down the inevitable, besides regular servicing and oil changes?

3. What should I be looking for in terms of noise/vibration/oil consumption(of which none happening yet)before I’m facing an engine rebuild or replacement decision?



Thanks in advance, Michael


#2

There’s a difference in sound between piston slap and an exhaust manifold leak. When you say “tick-tick-tick” that sounds more like a leak than the deeper sound made by slapping piston skirts IMHO. A good mechanic can make the distinction but they can sound very similar. Both would tend to clear up as the engine gets hot. A stethescope can be very helpful in determining where the noise is originating. My point is that we often fear the worst and continue to forge headfirst in that direction before doing everything possible to insure it is the right diagnosis. Did the Subaru service tech say with any certainty that it IS piston slap? What did they do to come to that conclusion?


#3

I might be leaning towards more of a valve lash problem. Look at the sticker underneath the hood and the owners manual about the specification on this.
Most car makers have extended the interval for inspection of valve lash on solid lifter engines to over a 100k miles (maybe a 105 on your car) in one of those efforts to make their cars appear to be more maintenance free. JMHO, but this is idiocy.
It could be that the noise goes away when the engine is warm because the excessive lash is tightened up due to thermal expanion of the metal. Car cools down, the gap increases, and you’re back to noisy lifters.

The valve lash would be my prime suspect anyway and have no idea why the dealer has not considered this except “valve lash out of sight, out of mind” has taken hold; which is exactly my point.


#4

Yes, another very good possibility!


#5

Subaru service tech said problem was caused by low oil, changed oil, kept car overnight, and said problem gone next morning. Problem back the following morning, however.

I think I will go to an independent guy next, and have him check valve lash and also for possible exhaust manifold leak.