I don't have a Dong Fang. I live in Hawaii on the Big Island of Hawaii. It is now 2:23PM, and at 2:15 we had a 5.something earthquake. Shook my house pretty good. Here I can easily run 15W-40 or 20W-50 even, as the temp never gets below maybe 60 degrees. When I lived in the Puget Sound area of Washington State one bike I had was a KLR650 Kawasaki. I rode in year round even down to 25 degrees. Once I tried 15W-40, instead of the normal 10W-40 I ran in it, and the 15W-40 made the bike have a very scary knock. Went back to the 10W-40, and no more problem. Harely's run 20W-50 even in the cold.