If your C-MAX was built before 29th July 2018 the service interval is one year or 12,500 miles (whichever comes first), and if it was built after this date then the interval is two years or 20,000 miles. However, the condition of your oil is crucial to the health and longevity of your engine, and the filter plays a big part in maintaining its condition. If you plan to keep your vehicle long-term, or just want to keep it in the best condition possible, we would recommend changing it more frequently, ideally every 5000 miles for the highest level of protection.