The owner's manual for many new vehicles still contain instructions on how to the "running in" of the engine should be done. This is provided by the manufacturer to ensure that all rotating and moving parts (in relation to each other) can settle optimally. The duration of this phase will typically be in km and optionally combined with time.
This phase is important to allow for the engine components to settle and adapt. The major components needing settling are bearings, crankshaft, connecting rods, pistons, piston rings and cylinder liner. The oil consumption might be higher during the running in phase due to the piston rings not sealing optimally and thereby allowing the oil to enter the combustion chamber.
A rule of thumb is a that a new/reconditioned engine should be run in during the first 1000 km. Best practice is to perform the first oil change after the first 500 km. Some engines can benefit from a special running-in oil and then changed to a multi-grade oil as recommended by the manufacturer.
The first oil change will ensure that dirt particles, swarf and sealant residue are flushed out. The second oil change would be considered as the end of the running in phase. After the second oil change, the recommended vehicle service intervals should be followed.
While the engine is being run in, the following criteria should be taken into consideration: