I was curious if anyone has done a scientific analysis of oil in small engines. I have overhead valve as well as the old style flat head type engines. I have been running Rotella T6 in my riding mowers with the Kohler Command and they seem to do very well on this oil. I run them hard and there doesn't seem to be any consumption as far as I can tell and the oil still looks clean when I change it. Both these engines came to me used consuming oil/smoked and with the hydraulic lifters clattering. There is no more of this and it went away quite quickly after switching to the T6. I figure this oil is the right one for these engines. I have been told the 5W40 might be too thin for some of the splash lubricated flathead engines. Many of these call for 30W. I also see ATV/motorcycle or marine oil with more additives for anti-wear. These are usually 10-W40 or 20W50. I was wondering if these would be best in these units as I don't need to worry about fouling the emissions systems as they don't have them. Then there are some that are splash lube yet have have overhead valves. Some of these even use PLASTIC camshafts these days. What is suggested as the best oil for these? I kinda liked the idea of a one size fits all 5W40 but correct me if I am wrong. I recently junked a Briggs plastic camshaft unit when the cam lobes finally wore down to where it would barely run after a decade or so have hard use.