Cold Idle/Engine-Brake Rattle

[gathermewool]

97 Subaru Legacy GT
203k miles
Auto Transmission
Rotella T Synthetic 5w40 W/ OEM filter

On most starts, regardless of temp the normal piston slap is very evident, and doesn't seem to ever fully disappear, but does diminish after the engine has been at normal operating temp for a bit. From what I've read, this is completely normal, and hasn't worried me.

For cold starts (ticking (can't quite describe it correctly) sound is evident. It's most noticeable while the engine is still cold during engine braking. It's definitely loud enough to concern me, but not so much since it does seem to slowly subside as the engine warms up, fully goes away when the coolant is >160F, and does not return until the next cold start.

It goes away when I hit the gas, even slightly, to accelerate or stop engine-braking. I thought this was the strangest symptom, but I'm sure it'll stand out to some one here.

I've used everything from Castrol GTX HM 10w30 to Mobil 1 High Mileage 10w30 to my current run of Rotella T Synthetic 5w40 over the past couple of winters, none of which seemed to make any difference. It doesn't occur at all during the warmer months so I can't tell for sure if the frequency, severity has worsened; however, I do think I'm noticing it more this year, so maybe it has.

Any ideas would be great.

 

[artificialist]

Does your car have hydraulic lash adjusters?

If not, you should take the valve covers off, and measure valve lash, then adjust if needed. Your car might have valve lash specifications listed on the smog equipment label. If not, find a service manual.

 

[mechtech2]

Probably in the valve train.
Certainly at 200k, parts are worn.
See if your car has adjustable valve lash.
If not, parts are simply worn a bit. Since this can be expensive to fix, you might consider living with it.

 

[gathermewool]

Thanks for the replies, guys! I believe HLA were introduced in 97, but I can't be sure. I'll research a bit more, and possibly take off the covers the next time I have a free day to get into the shop. The gaskets are weeping a bit, anyway. Maybe soaking the HLA in some solvent or bleeding them of air might help the issue.

 

[gathermewool]

I found a sound clip that's pretty close to how mine sounds. If you notice, you'll hear the piston slap when he revs, then a second noise when he lets off the throttle - THIS is what I'm talking about. Mine is as bad as his when cold, but sounds and runs perfectly normally when it's up to temp.

Subaru Piston Slap