engine air filter vs cabin air filter

[friendly_jacek]

I just replaced both @30,000 miles in my RAV4 and the engine air filter was very clean (almost new) while cabin filter was very filthy. This was also my experience in other cars with cabin filters. Why the discrepancy? Is the volume going through the cabin that much greater?

 

[BuickGN]

You figure a 250hp engine flows 300CFM or less at WOT. A HVAC in the car likely flows 300CFM but is flowing closer to it's capacity all the time.

 

[tenderloin]

Location of air intake. Also does the re circulated air go thru the filter? If so, another source of dust, pollen,smoke (if one smokes) etc
Smaller particles are filtered.
Fram site says down to 5 microns
http://www.fram.com/products/airFilters.php

Wix
http://www.wixfilters.com/productinformation/gff_cabinairfilters.html

Purolator
http://www.purolatorautofilters.net/products/Pages/breatheasycabinairfilters.aspx

 

[raytseng]

at 30k miles, I'd expect the engine air filter to be dirtier and not white.

My guess is most likely sometime ago the air filter was changed, perhaps without your knowledge.

 

[ThirdeYe]

It depends on the design of the filter and the application, I've found. Certain cars I've maintained have filters that get filthy fairly quick. On my car, even after 30k miles my filter didn't look that dirty and probably could've gone longer. I drive down dirt roads fairly often, too.