Knocking noise

Asked by Dtfalkjr Mar 07, 2017 at 12:40 PM about the 2007 Subaru Outback

Question type: Maintenance & Repair

When you drive my wife outback when you take
your foot off the gas you hear a knocking noise
from the drivers side of the engine anyone got any
suggestions

3 Answers

Could be piston slap, a rod knock or a worn wrist pin.

1 people found this helpful.
47,960

Cold or hot? If only cold: piston slap; if when hot rod knock. This one's old enough that replacing motor is out of the cards. Just keep coolant and oil up to snuff and don't over rev under load...you could get lucky and drive on this weak plateau for a long time. But if the knock gets progressively worse expect for the motor to crap out while running, at which time chasing a used motor would not be cost-effective given age. Good luck. Note that running synth oil won't help...neither will additives.

1 people found this helpful.
47,960

To be clear: piston slap self-corrects as motor warms and the pistons' travel becomes perfectly horizontal, so just don't over rev when cold; but usually it's only audible on acceleration...not decel. So I suspect you've rod knock at temp. You can verify also by warming motor and with quiet ambience just revving motor off idle, listening carefully for the knock.

3 people found this helpful.

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