Anytime you change oil, you should make sure that the engine has run for a minimum of 15 minutes to make sure that the oil gets hot. This will do two things, one the oil will flow much faster to cut the time it takes to drain the crankcase. Second, as the oil flows through the engine or it is splashed around the detergents in to oil cause the dirt particles to become suspended in the oil and will be removed with the oil.