After turning wrenches for over 40 years I hope I have learned some thngs about oil and such. In warm weather the heavier weights are good to use especially if you are really working that engine. If not a good 10-30 works very well or a good quality 30 wt. You might look at Lucas products which helps keeps things lubed when you first start up. I have seen more than one engine suffer from lack of lube when using 20-50 wt in cold or very cool weather as it takes too much time for the oil to circulate to the cam and such. Harder on the starter too. Also you use more fuel in colder weather as it harder for the oil pump to circulate that heavy oil so you need to put your foot further down on the pedal to get it moving. OHC engines really suffer when to heavy of an oil is used. They "knock" on the upper end until the oil warms up some. Anyhow, just my two cents worth. Henry