anyone notice a MPG drop when switching to different air filter?

I don't see how changing the air filter could do this. If anything, changing out a very dirty air filter might INCREASE mileage to a very slight degree.

 

I could see an aftermarket filter changing the air pressure - too much vacuum if the filter's got a lot more resistance, or too little if it's got a lot less. Not sure if the engine's capable of sensing the richness of the fuel mix and adjusting to compensate.

Did you put the stock filter in to verify mpg returns to normal, as a problem isolation step?

 

You get exactly what you pay for in air filters. I used to be heavy into tuning my engine and I could really tell the difference in air filters. If you buy some $15 STP airfilter, your just depriving your engine of airflow, and it has to work that much harder. If you can, find a K&N. I'm not sure if they make it for the Prius. I alredy ripped my whole air filter box out and ran a K&N cone filter directly to the throttle body. Integrate the mass airflow sensor and your golden It raised my MPG by at least 5.
When your buying an airfilter dont go cheap. Just bite the bullet and get the best one. You only buy then around once a year so why not?

 

It shouldn't change mpg, the air/fuel mixture is held constant like in all gasoline powered cars. The only difference would be filtering quality. If filter is dirty, air flow is reduced, so power lessens as less gas is mixed in. MPG may or may not lessen with less power. The original is a good choice, made by Denso, they claim it has three levels of filtration. I don't see why the STP one isn't adequate, supposedy made by Champion filters, and lots of cars run with those without problems.

 

<div class='quotetop'>QUOTE(Mr.Vanvandenburg @ Jun 18 2007, 11:35 AM) [snapback]463988[/snapback]</div>

Actually there is a mechanism that directly affects MPG. If the filter has a higher resistance to air flow, the engine has to do more work to pull the air through it ( Work = Pressure drop * Air flow rate). Just don't sacrifice filtering out the dirt to get lower air flow resistance.

JeffD

 

You are right. I was assuming any new filter would flow well. That may not be true.

 

K&N makes a replacement filter - Part #33-2329.

 

K&N flows great but has been known messing up the MAF due to oil getting on it, the paper filter filters better in dusty areas and does not cause problems with MAF, so there's pros and cons to both.