No, he does'nt have to drain the reservoir, all 2stroke oils will mix with synthetics 2 stroke oils. And BRP oils are manufactured by Castrol.A friend has a 550 cc fan cooled '05 GTX and wishes to use lower cost Castrol snowmobile oil.
Does he have to drain the reservoir first? Or can he just throw the regular Castrol oil in with the existing BPR synthethic oil?[/b]