Castrol Engine Shampoo is a treatment before oil change with a Powerful Cleaning Agent (PCA) that removes engine sludge * and collects dirt particles, so that they are easily drained and the engine is cleaned so that it is ready for new oil. It is intended for use in older cars with high mileage, but it can also be used in newer cars as part of the usual oil change to ensure that the engine always remains as clean as possible.