Arrow on aftermarket cabin air filter

Yes, fan is above, blowing air down through the filter. Confusion arises 'cause Toyota opted to indicate "UP" directions with arrow on OEM filter, whereas aftermarket filters have arrow indicating flow direction (sometimes ID'd thus, sometimes not).

Excerpt from Owners Manual:

 

yes.

 

Almost correct. How 'bout " ... fan is below, sucking air down through the filter. Confusion arises ... ". Indeed it does!

Showing "UP" direction instead of air flow direction was a needlessly confusing poor decision, in my opinion. What if they decide to use the same filter in another model in which the air flow is upward?

 

Still doesn't look like it makes a bit of difference which way it goes in.

 

Thanks for the clarification. I just assumed fan was blowing, doh.

One thing, air flow direction is not readily apparent when you pull out the glove box. The only was I can see to clinch it: both the air filter housing and the filter edge have similar labels, say: an arrow and the text "air flow".

 

agreed, the tell tale is the junk on top of the filter, which makes sense. otherwise, it would fall down every time the fan shut off.

 

On engine air filter, underside IS the dirty side.

 

Iff the fan blew into the filter, then the fan would have to eat the airborne junk first, which would be noisy, and possibly damage the fan.

Another easy clue: Below the filter, you can see the center of the fan. Air always enters centrifugal fans near the center and exits on the periphery.

 

i didn't think you could see anything. are you using a mirror?

 

Correction: It's been a few weeks since I checked out that filter, and evidently my memory confused what I'd learned about it through one sense with what I'd learned through another sense. By looking through the filter opening, you can see only a bit of the far side of the fan without a mirror, contrary to what I said earlier. However, by putting your fingers into the opening, you can easily feel much of the top side of the fan, and easily feel where its center of rotation is. Sorry 'bout the misstatement!

 

interesting, thanks! i'll have to stick my fingers in there. (surprised i haven't yet) i wish toyota would develop an easier to open and close glove box.

 

so finally, which’s arrow should point up or down when put it in? thanks

 

That really depends on how the filter is marked.

All we really know is that the airflow is from top to bottom when we are looking at the fan assembly in the car.

We don't know how "your" filter is marked. The key to the whole thing is how the filter is marked. Now, if it has the word airflow with a arrow next to it, then point the arrow down. If however the filter is marked up with a arrow next to it, then point the arrow up.

As other's said, you can consult with the manufacturer of the filter also if you still have doubt.

 

I can just about here the collective groan, but anyway: even though you can ascertain which side has the fan, does that determine the air flow direction, lol? I mean, it could be pushing or pulling?

Another, maybe helpful question: does it matter which side of the filter is up, as long as you keep that side up, consistently?

 

It wouldn't make any sense for the fan to be "pushing" air through the filter. If it were, all the leaves, bugs, and whatnot that the filter is supposed to keep out of the fan would have to pass through the fan first. Besides, you can feel that the center of the impeller is below the filter, and centrifugal fans always take in air at their center and send it out from their periphery.

Wasn't that easy!

 

The air flow arrow on the filter should point down when the filter is installed. There is confusion regarding the arrow on the filter access cover which is labeled "UP". The arrow on the cover is only there to show you how to reinstall the cover, not the filter. The air flow is down, so install the filter with its arrow pointing down.

 

Would the main thing be to just always reinstall it the same orientation? In other words: there's no optimum direction of flow, you just want to avoid reversing the flow of a used filter if you reinstall.

 

EXACTLY.

The filter is only a piece of paper. If you remove it for cleaning and reinsert it in the opposite direction, no matter how well you cleaned the filter, the fan will blow dirt throughout your car. Yuck.