What is this engine sound (video)

[Kario]

Happens every time the engine is cold and only when i push throttle. It is not audiable on idle. Then engine warmes up after a few minutes of driving it goes away.

 

The car is '00 legacy 2.5l with manual transmision. No turbo.

 

[ame=http://www.youtube.com/watch?v=SRRH7N4nZ8c]YouTube - subaru engine noise[/ame]

[Kompleks]

sounds like its not lubricated, try using synthetic oil.....

[mwiener2]

if it goes away after it warms up, it's probly just the normal boxer noises cept a bit louder.

[badbasser98]

As long as the noise goes away, this is normal. If it does not go away, then it is most likely piston slap.

 

I bought a used 2002 GT and it had piston slap fairly bad when I got it. Luckily it was under warranty still and I got a new short block compliments of SOA. All the 2.5l engines knock on a cold start. Nothing to worry about.

[arumis555]

That's so called "piston slap" - is normal behaviour for almost all subaru engines just after cold start. You can try to reduce this noise by playing with different oils -

as I remember on my old Legacy ( 1997) the best was Mobil Synth S 5W40 ( during winter time). If noise goes away on hot - do nothing.

But ,there is another story:

This sound could be recognised by knock sensor as real knock and ignition retarded by ECU. As a consequence of this - power "gaps" on some RPM ( around 2300-2500)

[Kario]

Are you sure its a piston slap ? This happens olny when I accelerate, i thought that PS is also there on idle.

What about timing belt tensioner issue, does it sounds like it can be the case ?

[scottmcphee]

it does sound low end and not top end to me..

I guess on a boxer I should rephrase that:

it does sound middle and not edges to me...

and I don't hear it on all four pistons, just one or two maybe

but it could be just one lifter getting a little sluggish

 

For fun do compression test and see if one is a lot different

 

Or maybe just pull one plug after starting, one at a time, and see

if the noise changes when you do this on one of the cylinders

[03LegacyWgn]

Hi guys, im a Canadian owner of a 2003 legacy L wagon with the 2.5 now i do believe i also have the piston slap/knock, now the car only has 70,000km on it and does it on idle when cold and not so much when warm at idle but i do hear a lil bit while driving, now is there any canadain members here that has had this problem and also would this be covered under any type of subaru recall or service bulleton? and also would this be something that i would want to fix asap or will the motor be fine just have to live with the sound?

[ehsnils]

Happens every time the engine is cold and only when i push throttle. It is not audiable on idle. Then engine warmes up after a few minutes of driving it goes away.

 

That sounds like a hydraulic valve lifter failure to me. Probably caused by a spec of dirt. I had that on my XT (see avatar), but as noted - went away when the engine got warm.

 

To be really sure you have to check that it isn't anything else which can cause serious trouble later. If you don't have any hydraulic lifters on that model (I know that it is different from engine to engine) it may still be a valve adjuster that's out of shape.

 

As someone suggested - a compression test is never wrong - it will provide you with a clear indication of if there are any more serious things going on. Anyway - it's hard to tell the sound from the recording since it's necessary to listen from several directions to be able to figure out where it originates. Modern engines are also very closed so that doesn't make such diagnostics easier. Sometimes it's possible to feel the knocking by touch too, which may help you to isolate - but look out for belts and fans!

 

Just for the sake of it - also check the alternator and other items. The easies way is to release the belts and check if the sound still is there.