One full 8 oz. bottle of Tufoil will be needed for an engine that uses 4 - 5 litres of engine oil.On subsequent oil change, a minimum of half a bottle is usually good enough.
Some people change their engine oil at 10,000 km. Others, 5000 or 7000 km. For our own cars, we have maintained a 5000 km change interval regime since 20 over years ago regardless of the kind of motor oils we use.