I had a terrible experience with Phillips 20W50, and then on several occasions with 15W50, in my O-200, and will never use either again in that engine. I use W80, because that’s what Continental says to use, and it works perfectly fine. I always preheat to assure an oil temperature in the sump of at least 45F before starting. My Lycoming O-360 came to me with 15W50 being the oil of choice, and...