How do you flush a car engine?

An engine flush (in regard to an overdue oil change) is an additive that is put into the crankcase. Usually these take 3-5 minutes of the vehicle idling to dissolve gum/sludge/varnish deposits that build up when you go over the recommended interval. There is much dispute as to whether or not this service is any good at all. Some recommend using transmission oil instead of a brand of 'engine flush'.

A radiator flush, or transmission flush consists of an exchange of the coolant, or transmission oil. These are usually performed with a machine that hooks into your hoses or lines and when your vehicle is idling, circulates the fluid through the machine and transfers new fluid into your vehicle. These are recommended by the manufacturer at specific intervals.