I certainly am no expert because Steve is, but that explanation does not sound right. these engines take like 20 to 30 minutes to cool down and by that time any weight oil has long since dripped down off cams and everything else. A zero or five weight has higher initial lubricity (sp?) allowing it to splash upward and around more quickly on cold start up than a 20 weight oil that in theory needs to warm up before it gets into all of the nooks and crannies. Also, my owners’ manual says 10w40 and my WSM says 5w40!