With the fuel that is sold these days around the country it seem like we need to change filters and clean out pre-filter about every 3 months. They are supposed last much longer, but after about 3-4 months our trailers start to starve for fuel because they are all plugged up. Sounds like there is a design flaw in how they recirculate fuel in these units and with the Bio Fuel mixed in to todays Diesel it does not work out well.