Spin on Fuel Filter Direction of Flow | Turbo Diesel Register Aug 22, 2016Silly question but which direction do the after market spin on fuel filters and water separators flow? I ask because I installed a CAT 1R-0750 and Baldwin BF1212 filter just shy of two years ago prior to installing new injectors. Part Number: 33840 - WIX Filters For reference only. There are no express or implied warranties with respect to products selected by size, feature or cross reference. Warranties only apply to products selected according to the Vehicle Application Listing.