Hello folks and how many of you folks here use either the Quaker State Conventional and Quaker State Ultimate Durability and like or dislike it? I have been using the Quaker State Conventional 5w20 in a friends car for oil changes. No complaints from him. My father will NEVER use it or Pennzoil conventional for some reason, as he uses Valvoline. Anyways, I did some looking and cant believe the "stories and old wives tales" bout it causing sludge etc. Thanks in advance for the replies guys.