The first time I replaced the air filter on my car after installing an Injen CAI, I found it to be a lot more dirty on the side of the filter facing the road relative to the rest of it. It even had 4 or 5 small rocks embedded in the filter itself. This made me a little uneasy, so instead of re-oiling it, I just bought a new one. I guess the tires, especially considering how sticky they are, just pick up little rocks and kick them around. I purchased and installed a splash guard not so much for the "splash" protection, but to act as a sheild from flying debris. I just checked it a couple of days ago (both filters had about the same time and mileage and were driven under the same conditions) and there is a huge difference. The filter itself is a lot cleaner with no rocks. You can also see from the water stains, that it prevented water from dripping on the element as well. These water stains are from car washes as my car is not rain driven. A small investment and easy to install.

 

You're from vacaville? I topped mine out right around there on the 505