If too much engine oil is added to a vehicle, parts of the engine may agitate the oil, turning it into a foam that cannot lubricate the components or carry away contaminants. Regularly checking to see that a vehicle contains the correct amount of oil as recommended by the owner's manual can help prevent engine damage.
One of the primary functions of engine oil is to reduce friction and wear on the vehicle caused by the movement of engine components, such as the crankshaft that spins. As oil lubricates the parts, it also collects contaminants, making it necessary to change the oil periodically.
Adding too much oil allows the crankshaft to dip into the fluid, whipping air into it and causing tiny bubbles. This turns the oil into a foam-like substance that no longer has the ability to flow and coat the engine components properly, so the vehicle is at risk of damage as the metal parts come into contact with one another, according to Motor Oil Matters, which is part of the American Petroleum Institute.
Additionally, if the vehicle contains more oil than it requires, the lubricant may burn within parts of the engine, leaving behind harmful carbon deposits. To prevent this, drivers need to use a dipstick when adding engine oil to the vehicle and ensure the amount does not exceed the maximum level marked on the stick.