Dear brothers according to ASME these oil codes only apply for colder and hot regions they don't have to deal with engine new and old. It's just the old myth we are running into by our mechanics. bad milage has no concern with oil, oil main purpose is to lubricate, cooling, cleaning and sealing. So of sealing is not ok you will see the smoke and your car start consuming oil. To check sealing of your compression system you need to take out compression test by some good mechanic. Clean the throttle system and then adjust the idle system
