From my experience with 3000 hours on my O-200, I will never again run any multigrade in it. If the temperature is close to freezing when I plan to start, I will properly preheat. I don't start cold engines, so I don't need multigrade. For my two Lycomings (O-320 & O-360) they seem to be more tolerant of multigrade. They were both operating multigrade when I bought the planes, though I have since changed them to straight 80, and again, am careful to preheat when appropriate. I did not find the operational difficulties with multigrade in the Lycomings as I did in the O-200, but I changed anyway to run common oil in all. With preheating and proper winter baffling, I do not find multigrade to be beneficial enough to overcome the added cost and difficulties with possible viscosity breakdown.