# Dirty/Oily air filter on new cars

**URL:** <https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905>\
**Category:** Maintenance/Repairs\
**Created:** [October 19, 2008, 10:55am UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905 "2008-10-19T10:55:02Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jake\_rome](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@jake\_rome](https://community.cartalk.com/u/jake_rome)\
**Post date:** [October 19, 2008, 10:55am UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905/1 "2008-10-19T10:55:02Z")

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Why is it that some new(and older)cars get this black dirt/oil buildup on the air filter?

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**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\
**Post date:** [October 19, 2008, 12:54pm UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905/2 "2008-10-19T12:54:33Z")

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Is it the engine side of the filter, or the free air side? This is somewhat normal on the free air side, as the filter is removing particles, soot, and crap from the air before it enters the engine. The engine side should be clean, except for extremely dirty filters. I’ve only noticed an oily film and soot on the engine side of extremely worn engines with a lot of blow-by. The blow-by will escape the engine through the crankcase breather line, and pollute the filter.

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**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\
**Post date:** [October 19, 2008, 1:05pm UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905/3 "2008-10-19T13:05:43Z")

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Could be a faulty PCV valve too.

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**Author:** ![jake\_rome](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@jake\_rome](https://community.cartalk.com/u/jake_rome)\
**Post date:** [October 20, 2008, 10:29am UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905/4 "2008-10-20T10:29:26Z")

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Its on the free air side and its before the PCV valve so how could this be? Ive seen it on a 6,000 mile Nissan Titan & a 7,000 mile Ford Exp. . . Where does the soot come from?

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**Author:** ![mcparadise](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mcparadise/32/32_2.png) [@mcparadise](https://community.cartalk.com/u/mcparadise)\
**Post date:** [October 20, 2008, 11:24am UTC](https://community.cartalk.com/t/dirty-oily-air-filter-on-new-cars/20905/5 "2008-10-20T11:24:46Z")

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It has to be coming in through the air intake. The environment in which such a vehicle is driven must be pretty bad, and the owner should probably follow the “severe service” maintenance schedule.