[Huxie]

Could they be referring to an engine flush perhaps? My garage always suggests a flush prior to an oil change as it’s supposed to clear out any sludgy deposits.

https://www.halfords.com/car-repairs...ELSERVICE.html

Q. Why can I not have the Fuel Efficiency Pack on its own without a service?

For this procedure to be fully effective, we have to apply it before draining the old engine oil and then refilling the engine with clean oil. By not draining the old engine oil after the procedure, any contaminates already present will remain in the engine and the benefits will be greatly reduced and it could potentially cause harm to the engine . It also makes economic sense to add clean oil to a clean engine!