Hi was looking at a 95 wrx on the weekend and the owner was complaning
of a slight knock when cold but go's away when hot.
sounds to me more like a crank knock than piston slap.

 

crank knock does not go away when hot piston slap does

 

As above - a worn big end/main bearing will stay noisy where as a piston should get quieter as it expands from cold.

Mick

 

It's only been doing it for about 3 to 4 weeks?

 

unfortunately, it's got to start sometime!

It'll Probably be less noticable as the weather warms up.

JohnD

 

The knocking go's when the engine is almost operating temp?

 

Classic piston slap behaviour.

JohnD

 

my 93 wrx does this. has done since i got it. it sounds just like a big end when cold. once warm its gone and runs perfect. kinda annoying but i can live with it. must admit, if i was a prospective buyer it would put me off.

 

piston slap