The semi-synthetic oil change is one of the more popular oil change options for Cadillac. A healthy blend of both conventional oil and full-synthetic oil, the semi-synthetic oil change is used to make the transition from conventional oil to synthetic oil. Cadillacs that have started to generate several thousand miles on their engine need this oil upgrade to maintain the performance in the Cadillac. This oil change option is also less pricy than the synthetic oil change option. 

The highest grade of oil changes, synthetic oil is one of the purest oils used for gasoline-fueled engines. It maximizes your engine's performance and keeps it durable long after it has to start aging with a generous number of miles. Any time a Cadillac has surpassed the 60,000-mile marker and starts to venture into high mileage on their vehicle, synthetic oil is recommended. It lasts longer than either conventional oil or semi-synthetic oil, giving you a little more mileage between oil changes. 

For the specialized Cadillac models that may house diesel-run engines, these motors' oil changes are used with diesel oil only. This specialized oil keeps the diesel engine calibrated and oiled up between changes just like standard engines and their oil changes. Neither semi-synthetic nor synthetic oil can be used for these oil changes. Diesel engines also have the ability to last longer between oil changes, with oil changes required between every 5,000 and 8,000 miles. These oil changes are a bit pricier than other options because of the specialized oil required.