Car #1 is a 2002 jeep with the 4.0 I6 and 18k miles. I have tried Purolator and Wix filters on it. Both must have drained back because it sits for 3 days and I could hear a loud knock that sounded like a rod when I started it.It went Clunk,Clunk,Clunk. Lasted about 5 seconds. I'm running 10w-30 amalie oil and a Purolater 14670 filter. #2 is a 73 International pickup with the I.H. 392 v8. Engine is a puppymill rebuild with 30k on it. With thin oil like 10w-30 it takes about 10-12 seconds to get pressure, it knocks and the lifters click untill it gets pressure. I ran 15w-40 Penns long life and a wix 51068 filter. It really took a long time to get pressure. I drained the oil back to sae 30 and changed the filter in 200 miles. I have straight Sae 30 Havoline in it now and a ST #43 oil filter on it. It will get pressure in 3 seconds after starting it with 30wt. It actully calls for the #8 Ford filter but I think that the smaller filter will fill up faster than the larger one. So I assume that the filters are draining back and I guess this is not good for my bearings. Both engines are spotlesly clean inside.Any ideas?