I know this may seem a little strange but it works well. I have used a concentrated toilet bowl cleaner. Drain the system and add a standard bottle of cleaner, refill and run untill the temperture comes up. Shut it down allow it to cool again (usually overnight) and run again untill the temp comes up. Allow it to cool again and flush with clean water, refill with coolant and you should be good to go. I have used this on several engines with great success, had to come up with something while deployed overseas and didn't have access to a standard coolant flush. It also leaves your engine smelling "Minty Fresh"
