Just check it every week or so. I changed mine when I still had the aibox about every 10K or less. If it looked dirty, I just changed it regardless of mileage.
-Ken V.
1998.5 SE Praire Tan Zetec ATX
psycho_bass@hotmail.com
Roush springs Roush rear sway bar BAT struts 17" Millie Miglia HT3 and a ton of subtle asthetic mods
