With the vehicle’s engine off, the 500-5100PD unit receives used coolant flow from the vehicle’s system through its RED hose and diverts the flow to an external waste container or to the shop’s coolant disposal system. At the same time, new coolant flow to the vehicle will be supplied from the CoolantClean™ III’s pump through the Green hose. It is recommended that vehicles (with conventional type coolant) have their cooling systems serviced every 15,000 to 30,000 miles, or according to the manufacturer’s recommendations. Periodic service intervals are recommended to provide proper protection against overheating and breakdown of the coolant’s protective properties. Old coolant can no longer protect against rust or acids that can breakdown metal & aluminum parts in the system. Have all the associated personnel study this Operators Manual to become familiar with the CoolantClean™ III Cooling System Service Unit & its proper operation.