BR tested a Purolator Boss PBL10241. The way it ranks in their test results is not how it ranks when looking at the official spec sheet from M+H, and also looking at the ISO 4545-12 testing that Ascent did which included a Boss filter.
Here's the official Spec Sheet from M+H for the Boss PBL10241. It shows the ISO 4548-12 efficiency to be 99% @ >46 microns. Ascent showed the Boss PBL22500 he tested to be 97@ 30 microns, but falls off to 63% at 20 microns. Do you really think that Boss is more efficient than the Fram Ultra? I don't ... it should be down around where the Wix XP and NAPA Platinum are ranked based on the official ISO efficiency specs. Also, the Fram TG which is ISO 4548-12 at 99% @ 20 microns should have tested higher in the ranks than it did ... another ranking that doesn't follow the official ISO 4548-12 spec ranking. So do you believe actual ISO test info, or info from a home made test rig that tries to rank the relative efficiency of the filters?
So this is why you need to take BR's "efficiency" testing with a grain of salt. When a filter they test doesn't rank nearly the same as if you ranked all the official ISO 4848-12 test specs, then you have to question the test methodology. BR has tried to come up with an "efficiency" test that works in terms of "ranking" filters, but IMO it doesn't seem to really work as expected when you compare their results to ranking by official ISO 4545-12 specs for the same filters.
I will say that the flow vs dP data they obtain is more believable in terms of ranking the comparative flow performance of the filters they tested. Keep in mind that the cold oil (500 cSt viscosity) flow vs dP testing is only good for flow before the bypass valve starts opening, so for only about the first 2 or 3 GPM at that thick viscosity.
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