Hello, I've been Googling this question but can't seem to find a solid answer. Should I use synthetic or conventional? 30W or 10W40 or 20W50 or ? I see the manual says 30W above 40F. Ok how about synthetic? I know i used 20w50 in my 22HP Kohler when I had a lawn service here before. I remember the mower shop telling me to use it. But this time I figure since I can ask online it would be nice to hear some input. I have 10w40 in it now for about the last month.