I recently switched from using castrol 20w50 to castrol 10w30. I noticed I am not burning up as much oil as before. I haven't change the way I drive. Anyone share the same experience? I guess it is either my OMP is not working or the different grade of oil is making the difference. How can you tell if the OMP is not working? BTW, my car is a completely stock 85' gslse with 68,000 miles. I premix with MMO.