Oil change in 2005 Passat 1.8t using O'Reillys 5w-30 Full Synthetic and wix filter. 66 degrees outside, RPM above 3k, 250 miles into trip engine shut down warning, low oil pressure. Oil level good, no foaming. Kept rpm below 3k, okay. 100 miles later, outside temp now 83 degrees, alarms again, can not travel freeway speeds. Limped in to oil change center. New change later no problems. Valvoline 5w-40, Mighty filter. Did oil viscosity drop or filter relief problem? Hard to say. Had similar problem when dealer used Dino oil w/o checking proper spec. Caused oil foaming and low oil pressure.