Review on K&N 33-2478 Engine Air Filter: Premium High Performance Replacement for Nissan Altima L4 2.5L (2013-2018) by Damon Blazis

This is the 4th K&N filter I have used on 4 different vehicles. The previous ones have been more than satisfactory and worth the extra cost for better mileage and protection. So far my 2013 Nissan Altima SL with 4 cyl. gets (almost) the 27 City/38 Highway mileage it claims: 26.2/36.6mpg. After driving 5,491 miles on the car's odometer, with the paper element air filter installed and driving properly and sensibly, I was pleased with the performance of the original filter. Even under ideal conditions, a vehicle rarely achieves its factory-specified EPA MPG. Before traveling to the Bay Area, California from southwest Wyoming, I purchased this K&N 33-2478 air filter to compare to a factory paper filter. trip), I never deviated from my I-80 route and stopped and stretched my legs (twice) for nothing but gas. Note: I have never had to buy more than 8 gallons of 87 octane gas at a time for an 18 gallon tank. My southwestern Wyoming is at home at nearly 7,000 feet. My CA endpoint is at 300 feet, so the move down is significant. However, I had to traverse part of the Unita (Wyoming), Wasatch (Utah), Ruby (Nevada) and Sierra (California) mountains for almost the entire trip, so it wasn't all downhill. However, the Altima SL averaged 42.4 mpg highway with the K&N filter, an average of 5.6 mpg more than the factory paper pad. All this at 65 to 75 mph on the open road. I had nothing but a medium-sized suitcase and a fridge for groceries. The return trip averaged 2.2 mpg less for the 800 miles home due to the 6,500-foot incline. The average overall increase isn't overwhelming, but it's a very significant increase that could pay off in a year or two. With gas over $4.00 in the Bay Area, I'll take it. It remains to be seen how clean K&N keeps engine internals clean, but if filters didn't keep engines clean we'd be hearing a lot about it in the news and high profile lawsuits. K&N engineers explain that it's not just the foam element that filters out the containment can, but also the special oil that coats the element that attracts and filters out more particles, creating a higher "free-flow" effect. It seems logical to me. I have never heard negative comments about these filters, let's see...?