A K&N Filter on a Toyota?

The K&N filter is a decent unit. While it won't do much of anything to improve hp on a Prius, it will last a while when properly maintained. The downside of a K&N filter is that you do not get the same small-particle filtration as do the paper filters; as a result you will get a little bit more dust into your intake - meaning you may want to pay attention to how well you service both the oil and the intake tract. Also, the oil on the K&N filters has a tendency to coat the MAF, meaning you should take a little time to spray down the MAF with a spray cleaner designed for electronic devices when you service the filter, or you may start having issues with the MAF air flow read. The K&N should be regularly cleaned and re-oiled - don't confuse its durability with its ability to maintain good airflow parameters when dirty!

Another problem that you may have is that the K&N can cause the MAF to "mis-read" if its too close to the filter. If you have a drop-in unit into the stock Prius box there's not a problem; but if you use the unit on a CAI intake, you can have a problem where the air flow is mis-read, and the resultant fuel-trims are off. Like I said, this is generally only with the aftermarket intakes - don't worry if its a drop-in unit.

It's not that it's no good, but your engines program (ECM) will compensate for any changes in air temp and density. Thus it's a waste of money. Yes paper filters wear out. But if Toyota thought for a moment that K&N was a better filter, it would have come from the factory with it.

The K&N filter doesn't filter very well and lets dirt in which will wear the engine out. You could change your oil every 500 miles, but that's way more expensive than a paper filter.

There's nothing wrong with a k&n filter. Its just a lot of hype to making your car faster. Its just a cleanable type filter that you can use over and over. The problem comes in because you have to lightly oil it after your clean it, which can lead to a dirty build up on your mass air flow sensor. Long story short just buy a low price puralator or fram filter and replace it on a regular basis.

the oe style filter gets dirty because the area you drive is dirty, a K&N gets just as dirty just as fast and is not the best option for a prius, much like the first answer stated, also, when the filter needs cleaning the cleaning kit will cost close to the same amount as a replacement conventional filter,