مرشح بديل غير مطابق مركّب

A filter of the wrong specification fitted — the right size and the wrong element. Filters differ in more than dimensions: media grade, bypass valve rating, anti-drainback valve, and for a fuel filter the water separation capability.

A fuel filter without the correct separator passes water to the high pressure pump, which is the version that costs a fuel system. An oil filter with the wrong bypass rating either restricts flow or lets unfiltered oil through permanently. The part fits perfectly, which is why this survives inspection. Check the part number against the vehicle rather than against what came off, since the previous filter may itself have been wrong, and be sceptical of a filter that costs a fraction of the others on the shelf.