Subaru Noises

This page catalogs noises or unusual sounds identified by owners of recent Subaru cars, in particular the Legacy and Legacy Outback models. The information is collected from Internet message boards and as such may not be perfectly accurate and may change without notice. Attempts are made to credit posters and collect official documentation and solutions to help owners build cases for repair or to educate owners on the effects of commonly observed noise problems.

For updates, clarifications, or general communications about this page contact the author, Doug White.

The infamous "piston slap"

Summary

  • Description: Clicking, tapping, or knocking noise eminating from the engine after a cold start. The noise lasts until the engine is warmed, usually 5-15 minutes. The sound may be heard in the passenger compartment.
  • Affects: 2.5L DOHC engine, particularly from 1997 to 1999.
  • Diagnosis: The pistons are engineered for operation at temperature. In an effort to save weight in the engine, the piston skirts were shaved down. When the pistons are cool, however, they do not have sufficient contact with the cylinder to keep from 'slapping' or rattling against the cylinder sides. At temperature, due to thermal expansion, the pistons match up properly with the cylinder and do not rattle.
  • Reported solutions: In some cases, SOA has rebuilt the engine short block, while in others SOA prescribed "countermeasure pistons" with longer skirts that do not slap. Most dealers will initially state the sound is "normal."
  • Detrimental effects: SOA has said that the noise causes no engine problems or abnormal engine wear; Subaru engine expert CCR Engines of Colorado has said that the engine may experience a 10% reduction in life.

Anecdotal Data

Message boards:

Excerpted discussion (from USMB):

My question:
1. Is this piston slap detrimental to the engine? If so, then in what way? (By "detrimental" I mean engine life, as in abnormal wear of internal parts.)
2. If one should choose to take this up with the dealer/SOA, what would be your strategy? (Read: Is there a TB or other documetation on this problem one can use as leverage?)

CCR's reply (mixed with responses from a question about the oil pump):

Sorry guys: been really busy lately and when I tried to answer a couple of nights ago, my answer disappeared into thin air! (arrggh!) So, sitting here in greasy sweatshirt...
1) Both the 2.2 and the 2.5 have the problem with the screws backing off from the back plate.
2) Piston slap/wrist pin noise is not usually detrimental. Will it shorten engine life? Oh, maybe from 200K to 175K. It's mostly just damn annoying!
3) There are no replacement pistons that I know of. SOA gets a factory shortblock, puts your heads and everything else on it (then sells us the shortblock, cheap, to rebuild! teehee)
4) If damage is going to occur from the oil pump problem, it could be immediate or over 100K miles: there's no pattern.
5) Best thing to do is put a manual oil pressure gauge on and see what the pressure really is.
If your noise doesn't disappear when the engine warms up, I would think there is a collateral problem. Bitch, bitch, bitch! To your dealer that is. Keep it up until they do something.
Hope this helps: let me know if you have other questions.

Emily
www.ccrengines.com

Another user mentioned that I should get the noise at least documented under warranty. That will certainly happen at the 30k service interval.

Someone was able to get replacement pistons instead of a rebuilt short block:

In regards to piston slap, there are replacement pistons made by SOA to fix the problem. I know because I had them installed on my 98 Forester(same engine as the OBs)

On cold startups, I would get a distinct metallic knock that was different from the solid lifter noise. To make a long story short, I complained and complained and finally met with the district technical manager. He offered replacing my pistons with "countermeasure" pistons. He even showed me a memo written by SOA explaining that the slap is a result of the skirtless pistons and will not harm the engine. The memo goes on about if the customer complains enough, then use these countermeasure pistons.

I didn't get to see how the pistons were different but the fix completely got rid of my piston slap. That was 30K miles ago and my engine is running as smoothly as ever.

Steering rattle

Summary

  • Description: Loud thunking and/or rattling coming from the steering or suspension components during turns into a road depression, such as a driveway or off the pavement to a highway shoulder. In some cases it may be felt in the steering wheel.
  • Affects: 1995 to 2000 Legacy & Outback, or any 90s Subaru with the rack & pinion steering system.
  • Diagnosis: Current theory states that it is caused by components internal to the rack & pinion steering system shifting as the suspension absorbs the bump.
  • Reported solutions: No official solutions. Dealers usually say the sounds is "normal." One owner has found that spraying a rust preventative on the suspension components deadens the sound.
  • Detrimental effects: None known.

Anecdotal Data

Need to go collect some...