That is the common conception but on some Libertys at least they sometimes, but not always show low oil pressure after partial/full warmup at idle. Never did isolate the problem other than it was only with Fram or rebadged Fram filters. Could be a bypass valve not seating correctly ???? Fram cost $3, Wix cost $7. I use about 4 a year on each car so the added cost is less than $20 on a $25,000 car .. seems a no brainer to me just like synthetic oil changed at dino oil intervals. I was not the only one that had the problem.