Should i use K&N Air Filter or not?

I am using one so I vote Yes. Just make sure you don't over oil after cleaning.

 

Depends on your reasons and expectations for the filter and your car.

1. It is unlikely to improve efficiency (mpg) since even K&N doesn't make that claim.
2. However, it should improve ICE horsepower at wide throttle openings. (K&N does dyno tests on some vehicles as have other organizations.) Don't expect miracles from a drop in filter, just a few percent more horsepower. To me this would make sense in mountainous terrain where WOT is required and where atmospheric pressure is reduced anyway.
3. It is unlikely to filter the tiniest particulates as well as a standard filter. So all else being equal the ICE is likely to experience more wear over the very long haul. Having run with such filters for 100,000+ miles on each of two other vehicles I did not have any problems. K&N has a warranty for their filters.

 

This question has been around for a long time. The only obvious advantage (in Prius) is not generating a pile of used paper filters over time. My used engine oil analyses suggested that the KN did allow slightly more silicon (ingested soil particles) in the oil, but that was not accompanied by an increase in engine wear metals. It would make sense to watch for that.

In 2001-2003 Prius the air flow sensor is directly under the air filter, so the risk is real that an overoiled KN could drip on to the MAFS. You wouldn't want that to happen.

 

I still can't vote one way or the other on this as the OP has never come back to explain what he wants to accomplish with the filter. This is somewhat like comparing tires...what one is optimizing for determines the appropriate answer. (Snow tires don't make a lot of sense in Houston, and summer compound tires are not the best choice for Winnipeg in winter.)

 

I have used one for the last 80,000 miles, and have had no problem. I agree with others who say you will not get better mileage with one, but they are easy and cheap to clean and re-oil.

 

They work fine for reuse, but you need to clean and oil them each time at roughly the same interval as you would a filter change. There is some cost associated with that. When I used them I would wash mine from inside out with a hose and cleaner solution. Then I would let it drip dry after shaking water out. After that I would apply the oil and let it stand for an hour or two, wiping excess oil once or twice. Never had any problems with it.

Some folks point out that over oiling can get some of the material onto the mass air flow meter, I never had trouble with that in my 240. The Prius model already has some established trouble with crank oil and other material getting into that area, so one would be hard pressed to blame anything on the filter oil.

MPG wise don't expect any improvement. You might get some improvement, get none or even see a decline. Getting improvement that way would be more dependent on your driving habits than the filter. K&N is careful NOT to make a claim about MPG (various afficianados are not ). The reason is that the gains in reducing air flow restriction are typically taken up by the throttle valve. The exception is at or near wide open throttle. In a Prius WOT is rare.

I will probably install one eventually, I've just not needed the extra horsepower so far. When I finally take the car into the mountains, I plan to have one in place.

 

Can't say as I've not used one on this vehicle, plus this a drop in to the existing box. The ones I've used on other vehicles actually replaced the filter box.

More realistically one might hope for about 2-3 hp since this is only a 76 hp engine to begin with.