85 plus a small amount of force applied by the filtered oil 95 of the cylindrical cavity 80 to the first end surface 195 of the piston 140 exceeds the force applied to the flange portion and seal by the filtered oil 95 within the inner chamber 130 plus whatever drag force is imparted by the o ring seal interfacing the housing portion 125 by a specific amount determined by the force applied by the spring 145 then the piston 140 is forced away from the cylindrical cavity 80 in the embodiment shown forced upwards such can occur when the oil filter 45 is excessively clogged such that it does not allow oil to sufficiently easily pass through it as the piston 140 is forced upwards a top 215 of the piston is exposed as an indication that the oil filter 45 is excessively dirty clogged such that the oil filtering device 10 or at least the filter itself should be changed in some embodiments a color of a second end surface 212 of the top 215 of the piston matches that of the surrounding portions of the top of the filtering device 10 e g black while a side surface 217 of the top has a different color e g red such that exposure of the top is readily apparent further as shown the filter status indicator 50 includes a latching mechanism 220 that locks when the piston 140 is urged sufficiently upward and the top 215 becomes sufficiently exposed in order to lock the piston in place so that it cannot return to its retracted position e g move back toward the cavity 80 even though the pressure differential between the unfiltered oil 85 and filtered oil 95 might later fall.