Straight 30w oil is thicker at low temps than 10w30. The advantage to multi-viscosity oils such as 10w30 etc. is that they flow better at low temps, which means your engine gets oil faster on a cold start. The disadvantage is that the additives in the multi-vis oil tend to break down over time, which means that if you don't change your oil often enough or you get it too hot (that could NEVER happen with an air-cooled engine!
) your oil will thin out and you could have lubrication problems. Hope this clears it up for you. :wink:
Mike