i use to use valvoline but ever since switching to penzoil i notice the oil works alot more
when i change the penzoil out its black as night vs the valvoline looking like brand new when changed. this indicates that the oil is removing contaminants.
penzoil high mileage as with most high mileage oils are synthetic with additivies to prevent burn off
10w30 in winter
10w40 in summer