"The usual Ford oil filter has a bypass valve bult into the filter which can allow unfiltered oil to bypass the filter, and the bypass can also fail causing a loss of oil pressure. Consider using Purolator L30119, it's a full size replacement for the FL-1A Ford/PH8A Fram filter. It has no bypass spring in the middle but it does have the rubber flapper for anti-drainback. The original application is for a 1978 Nissan 510 L20B engine which had the bypass valve in the engine block. The Purolator L30119 cross-references to; Fram PH2850, Motorcraft FL-181 and Wix 51452, however these filters have not been verified and may still have the bypass. It appears after 1978 Nissan went to a half height filter, Purolator L22167 fits that application and does not have the bypass spring but does have the rubber flapper for anti-drainback."
~ Dan Jones
there'll be phantoms, there'll be fires on the road... and the white man dancing