verslagen1 wrote on 08/22/10 at 13:22:02:the owners manual says 20w50 is ok for higher temperatures.
I think it'd be better to have 10w40 during the winter, and 20w50 during the summer.
That's exactly what I do. That one morning when it was 15F outside last winter, I checked on that half full bottle of 20W-50 Lucas I had stored on the front porch, and when I opened the bottle it seemed pretty thick, almost like gravy what was inside. That's why I put 10W-40 in the bike in winter. But I use The Mobil1 stuff, as the Lucas 10W-40 is only semi-synthetic. I used the 10W-40 in summer also when I first bought the bike, but In 105+ heat here in Oklahoma there was a lot of valve thrashing going on, despite the valves adjustment. Especially since there's quiet a bit of in town riding going on, I didn't trust that stuff. Ever since I use the 20W-50 in the summer heat, the engine runs way smoother with a lot less thrashing. So when it gets to mid October, I put the 10W-40 in and run it until April.