Q: When I checked the oil on my car it was about halfway between the ADD and FULL mark. Should I add the half quart of oil now or should I wait until it reaches the ADD mark?
A: It makes sense to keep the oil at the full mark. Many engines today only hold four quarts. If you allow the engine to get to the ADD mark and your engine only holds four quarts of oil, you are running the engine 25% low on oil. Keeping the oil at the full mark helps in lubrication, dispensing the contaminants through a larger volume of oil, and disperses the heat more efficiently. Just be sure not to overfill the crankcase. Too much oil in the crankcase can cause foam to form if the crankshaft whips the oil, lessening lubricating qualities.