OEM filter is the standard we’re using to judge the other seven filters. Based on this standard, the quality of the Replacement filter is patently and grossly inferior, the next most inferior is the Ginza Japan filter. The anti-drain-back diaphragm on the Replacement filter is of very poor quality, so poor that it might even allow unfiltered oil back into the engine the same way it came in. Hence, at the very first stage of a filter’s function, the inferior quality of the anti-drain-back diaphragm on the Replacement filter has already given an indication of how poorly it will perform. Moreover, its poorly assembled filter media as demonstrated by the loosely and highly irregular pleat spacing indicates that it contains far less filter media compared with that on the OEM as well as that of the Vic filter. Because the Replacement filter and the Ginza Japan contain less filter media they consequently must have a diminished ability to filter dirty oil. And finally, under conditions where the by-pass valve will come into play, its by-pass valve has only one .8cm hole for the oil to pass, and the spring on its valve has a resistance that’s nowhere near as stiff as that on the OEM valve.
In the area of the filter medium, the best was that of the OEM Honda filter which seemed to be of paper/cotton blend. The worst was that of the Replacement “Mazda” and the Ginza Japan filter both of which had very irregular pleat spacing and a smaller filter area than the standard. The Power Long filter was the most unusual being made of stainless steel mesh. It would be much better to subject the different filter media to a genuine test to see which filters the best.