It's a long time debated topic, over time with sludge developed during the engine life is not a small matter, with latest engine oil technology all manufactures adding essential additives to keep the cleanness of engine oil during the operational life. even though sometimes we unknowingly extend our oil change interval resulting in developing sludge inside the engine while you are removing the engine oil the old engine oil won't go out in full amount. the leftover will stick to the walls of the engine in hard form. one or two-time leftover won't make any issues directly. after a few numbers of an oil change, the accumulated old oil content will directly start effecting. you can check this. add a new engine oil any time and ride your bike for 400-500 KM and check the oil condition. The colour turns to be black if the oil is in the black condition that means the old oil leftover that sticks to the wall of the engine is diluted with new engine oil. so slowly the engine oil property will start to change. Also, you can use this test as a recommendation, if the oil color changes to dark black in a few hundred km, so with the next oil change you need to use an engine flush.
How to use flush?
Liqui Moly engine flush is made out of petroleum detergent it won't affect the sealing, gaskets or rubber/silicon parts of motorcycles with good service history or new motorcycles within the life span of 5 years. It's important to know that everyone can't use engine flush, engine flush usage is subject to follow certain conditions, a motorcycle with less know the history or not maintained properly or engine older than 5 years must avoid the engine flush.
Add one bottle 80 ml ( sufficient up to 2.5 litres) start the engine and keep the engine in idle operation condition for 10 minutes (maximum don't exceed this) once the recommended time is over in idle mode switch off the engine, take necessary precaution to open the dry nut, remove all dry nut (main oil chamber + secondary chamber) it's mandatory to remove the full engine flush content before adding new oil. once the old oil is removed fully from the engine, replace the oil filter, clean the oil magnet. Now you are good to add any brand of oil.
High-performance engine oils + additives are tested and used on all type of motorbikes, Liqui Moly Engine oils are the exclusive lubricant of Moto2 & Moto3 Of MotoGP world championship, All Liqui Moly Products are manufactured in Germany.