Motorcraft FL-1hp pressure drop

[madmaxx]

I have been looking at oil filters. Many filters are practically useless (or I thought) because they have a dirty side bypass. In other words, the bypass is at the base of the oil filter and if the bypass opens (normally 9-11 psig differential across filter) it flushes the dirty side of the filter media into the engine. Ford Motorcraft on the other hand has a clean side bypass, it is fantastic design. I have no idea why all filters would not be designed this way.

I decided to determine the pressure drop across my new FL-1HP oil filter with Mobil 1 10W40. The FL-1HP ($14.99) bypass activates at 22 psig, as compared to 11 psig for the standard FL-1A ($3.79). Since I have a remote oil filter adapter with two extra ports it was rather simple. I just installed a gauge on each side, then swaped the gauges from side to side to ensure accuracy.

I was blown away to determine the pressure drop across the filter is under 3 psig once the oil hits 80C or higher. Even at start up with cold oil the differential was only 4 psig, outside temp 85F. The bottom line as long as you oil filter media does not get damaged, you are filtering 100% of you oil all the time!!!! In the end the regular FL-1A would suffice as would most oil filters since the bypass is unlikely to open at least above 85F ambient temperature.



Engine is a 351 with a Melling high volume oil pump.