5.3/6.0 GM V8s plugging up oil filters, oil pressure dropping to near zero. Why doesn't the oil filter bypass valve open preventing the drop in oil pressure? Hello, Roy Gage from Estherville Iowa where I run a small automotive repair shop. I will tell you what I know, what I think I know, what I think I do not know and then hopefully someone here can enlighten me. Couple months ago we had a 6.0 ¾ ton GM pickup in with about 195K on the odo. Ran nice, engine sounded solid. Complaint, low and at times no oil pressure. Oil pressure gauge in the dash was slow to come up and at times would drop to near zero. We replaced the oil sender, located behind the intake, and the small screen under it. No difference. We had previously swept test the oil gauge and knew it was working well. Replaced the customers PF48e AC Delco filter with a wix 57060, changed oil to 5/30 Dexos and all is well. Twenty plus lbs. hot idle, 40 plus lbs. down the road hot. Pulled the old oil filter apart. On one end of the pleats some sludge back about a ¼ inch back up from the end. The rest of the filter appeared good but when dragging a finger nail down between the pleats you could feel some carbon grit. To my mind this filter was not plugged to the point of restricting oil flow. I do now believe that it was. The customer had replaced the filter a month before then went on a two week vacation leaving the truck at home. Point is there were not that many miles on the oil and filter. If it was plugged it was simply because there was enough grit floating around in the motor to get swept up and into the filter. Customer told us he has used the oil life monitor for his change intervals since he purchased truck new. I contacted our AC Delco vendor whose manager told me another shop in town had trouble with the PF48E doing the same thing. He also reported he had trouble with them plugging up twice on his own truck. Sending a couple in to Delco he got back a report that there was no problem with the filters although I believe they must have told him they were plugged up as when the manager told him the Wix resolved the problem the Delco fellow said, rather sarcastically, to be sure to give him a call when his Wix plugged up. Found a lot of reports of others having the issue. Getting 2 or 3K on a change and then the oil pressure getting soft. At the time I blamed the Delco filters assuming they had a bypass valve that simply was not opening up. I also blamed, and still do that GM simply did not put a large enough filter on these motors to run extended oil changes and also that the extended oil changes were causing a carbon buildup in the motors. Victim number two. 2009 GM pickup with a 0 code 5.3. 160K on the odo. 7000 miles on a dexos oil change. Runs and sounds solid. Pretty much zero oil pressure at all times. Put on a sender and the screen below it, oil pressure slow to come up on start up but then OK. Took for test drive and pressure dropped to near zero after several blocks. Dropped oil and filter. Should note this one was equipped with a WIX 57060. everything is fine. Hot idle, 32 lbs. Down the road hot, 42lbs. In passing gear hot, 52 lbs. Cut the Wix apart. No sludge on the end as the Delco had, same light grit in the pleats. Again although this filter was dropping the oil pressure to near zero had someone asked me if it was plugged enough to drop the pressure before I ran into this problem I would have told them no. I have read some posts here about people reporting what their filters look like inside after 10 or 15 k and basically saying they look great. I will point out that after looking at these two filters, I would not be so sure about that. My burning question, which Wix's hotline was unable to answer and the technical hotline I use was unable to answer is simply, how could the filter's bypass valve not open? With forty lbs. plus on one side of the filter media and next to zero on the other how could a bypass valve Wix says is set at 12 lbs. not open and balance the pressure? Had you asked me before these two trucks I would have told you with the greatest of authority that upon the oil filter plugging the bypass valve would open and the event would be so seamless that you by watching the gauge would not be aware of it happening. Now I simply scratch my head. Yesterday I went to an evening clinic. Lots of techs there, most had ran into the problem. None had an idea of why the relief valve was not working as I thought it should. There is a SI bulletin from GM, #PIP5276D which tells you if you run into this problem, it will also set a code P0521,to upgrade to a UPF48R filter. I would be interested in what the difference is between the this number and the PF 48E. Now you know what I do and don't know, enlighten me. Thank you in advance for any insights. If I missed a pertinent discussion on the subject in the archives I apologize for the rehash.