# Piston slap...is it a concern?

**URL:** <https://community.cartalk.com/t/piston-slap-is-it-a-concern/12970>\
**Category:** Maintenance/Repairs\
**Created:** [April 17, 2008, 3:08am UTC](https://community.cartalk.com/t/piston-slap-is-it-a-concern/12970 "2008-04-17T03:08:25Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![batman](https://avatars.discourse-cdn.com/v4/letter/b/9fc29f/32.png) [@batman](https://community.cartalk.com/u/batman)\
**Post date:** [April 17, 2008, 3:08am UTC](https://community.cartalk.com/t/piston-slap-is-it-a-concern/12970/1 "2008-04-17T03:08:25Z")

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My 2005 subaru impreza makes a knocking sound when the engine is cold. The noise goes away when it heats up and the dealer says it’s “piston slap” and it is normal. What can I do?

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**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\
**Post date:** [April 17, 2008, 3:19am UTC](https://community.cartalk.com/t/piston-slap-is-it-a-concern/12970/2 "2008-04-17T03:19:43Z")

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Subaru engines have always been pretty loose…I have owned several of them, used them for a Colorado rural mail route. They all clattered a little. Piston slap is pretty harmless and usually will not effect overall engine life. I would use 10/40 oil in the summer and 10/30 in the winter…Maybe even a little “top oil” in the gasoline. 4 ounces of outboard oil per tank of gas will help lube the top end and avoid “dry starts”…Don’t race the engine until it warms up…