Shell Helix’s high mileage semi synthetic 15W-50 is especially tailored for old cars with high mileages. Its special formulation contains additives to provide up to 40% better wear protection so you can prolong the car’s engine life and keep it chugging along. Some additives such as zinc are found in the oil, which helps to prevent oil sludges and other damaging deposits. Moreover, the oil also contains a seal conditioning agent to prevent leaks and oil loss.