Originally Posted By: steveh
Tough Guard on page 4 looks very restrictive.
If you read the first post in that delta-p testing thread, you see that they are using room temperature oil and setting the flow to obtain 40 PSI on the inlet side of the filter. I haven't read every post in that thread, but I think they later on tried to modify the test to try and control the flow rate to be the same through all the filters, which is the best way to compare their flow resistance at a fixed flow volume and oil temp/viscosity.
If they were just adjusting the electric motor that drives the positive displacement oil pump to achieve 40 PSI on the inlet of the filter without controlling the flow volume, then the filters that showed a larger delta-p might have had a lot more oil flow going through them, and that was the cause of the larger delta-p.