Yamaha ULTRAMATIC GRIZZLY 660 2001 Manuel Du Propriétaire page 134

Engine oil
Make sure the engine oil is at the specified level.
Fill with oil as necessary. (See pages 8-33–8-45
for details.)
Recommended oil:
-20˚ -10˚ 0˚
5W/30
Recommended engine oil classification:
API Service SE, SF, SG type or higher
5-15
20˚ 30˚ 40˚
10˚
10W/30
10W/40
15W/40
20W/40
20W/50
EBU01180
50˚C