According to the user manual and depending on temperature they indicate the following oils SAE viscosity ratings. 20w-20, 10w-40, 10w-50, 20w-40, 15w-40, 20w-50, 15w-50, 5w-20, 5w-30. Seems that 5w-20 and 5w-30 will cover from -20F to +100F (-30C to +40C).
It states in the manual "Engine oil viscosity, or thickness, has an effect on fuel economy and cold weather operation (starting and oil flow). Low viscosity engine oils can provide improved fuel economy and cold weather performance. But high temperature weather conditions require a higher viscosity engine oils for satisfactory lubrication."