Need flushing advice

[medtro]

How long do you normally wait after draining the coolant, for the engine to cold down before rushing fresh cold water into the engine? Assume outside temperature is 80F-100F and fresh water is tab water.

 

[RavenTai]

I have no Idea if this is correct but is what I do: at least an hour, or until you can touch it, if you hear creaking it was to hot