I typically run a slight variant of this procedure for flushing my radiator: http://forum.ih8mud.com/showpost.php?p=1614118&postcount=4 One thing I've always wondered is how long to let the vehicle cool down before draining and filling again. I know its not a good thing to drain a hot engine and refill with (cool) fluid. There will be the temperature shock to the block just from filling with cool liquid amongst many things that could go wrong. Not to mention HG problems. A friend of mine cracked the block on a VW by draining a hot engine and filling with cool liquid. I typically wait an hour before draining the coolant from a hot engine. Sometimes I think an hour is not enough. Some of the posts I have read on radiator flushing don't mention a cooling time. So, I'm assuming they don't wait at all. How long is a good time to allow a hot engine to cool before a drain and fill?