OK, I have been reading for the past couple days triing to get up to speed so I am sorry if this has already been suggested.
After reading all the presure drop info on all the different brands of filters and doing a little research on the bypass valves, I think what we may be looking at is the factory set bypass presure. The few that were extreamly low may have been leaky valves or defective springs. The majority seem to be right at the generally speced 8-11 lbs bypass setting. And possably the higher ones have been set higher to try and force more oil through the filter media when it does get warm or to compensate for the higher restrictions that may be caused by the finer media catching more crud and shortening the filter life.
The warm oil test or maybe using water as the liquid would give more insight to the filter media restrictions.
After reading all the presure drop info on all the different brands of filters and doing a little research on the bypass valves, I think what we may be looking at is the factory set bypass presure. The few that were extreamly low may have been leaky valves or defective springs. The majority seem to be right at the generally speced 8-11 lbs bypass setting. And possably the higher ones have been set higher to try and force more oil through the filter media when it does get warm or to compensate for the higher restrictions that may be caused by the finer media catching more crud and shortening the filter life.
The warm oil test or maybe using water as the liquid would give more insight to the filter media restrictions.