Looking at my filters today and after removing the foam pre-filter it only filters the air that comes in from the engine compartment and not the actual main outside incoming air, so after the incoming engine compartment air, it still goes thru the main air-filter, just seems sort of useless to me.

 

it filters out the big stuff such as bugs and grass. kinda like the pre-filter on a lawn mower.

 

suppose to be for winter use primarily is my understanding.

 

there was nothing on the foam but several big bugs on the main filter and in the bottom of the airbox.

If it's for winter then there must be a diverter door in the main air tube somewhere, otherwise the air will take the easiest route in which will not be thru that foam.

 

I thought it was there in case the paper filter plugs with snow?

 

Noticed you have a 15 Ram in your sig. you on the right 6.7 forum

If that's the case it sure won't get much air the way the airbox is divided, only about 3" of filter available. That foam stills looks useless since only engine compartment air goes thru it and it still has the main filter to go thru also.

 

Steve is right. when you use the truck to plow the main paper element can get plugged if conditions are right. the foam pre cleaner allows air through the small section of the filter, when this happens.

 

What you are saying makes sense but if the paper gets plugged with snow/wet would this not ruin the filter?

 

no, it seems to hold up. mine got plugged when driving two hours through a blizzard last year. wasnt even aware this happened until next spring when I was doing my maintenance and saw that the filter minder was stuck at 100% plugged. thats also why in normal maintenance you change your filter, the small end will almost always be clean because it only gets used when the normal side gets plugged/blocked as that path is more restrictive.

 

There was a TSB from FORD to install one in winter regions. It is designed to filter out the snow from airflow . Without it the filters would turn into a block of ice when snow gets up into the filter region and you would gradually lose power at highway speeds until down to idle. Now I guess they all have?