Running-in a newly rebuilt engine is essential for its performance a long service life. Rebuilt engines require the pistons & rings to 'bed in' to the cylinder bores to give the correct sealing characteristics. Failure to correctly run-in the engine may cause glazing of the cylinder bores, which leads to excessive oil consumption, possibly requiring further disassembly & rebuilding of the engine. This oil is specially formulated to allow the correct bedding in of the engine internals, particularly the piston and cylinder bores. Running in oil is recommended for the first 500 miles (800 km).