Radiator Flush Now or Later

[90eliminator]

I am going to upgrade my cooling system to the open system, but should I flush the system before I do the switch, or just wait and do it after....opinions? Thanks

[Comanche County]

Umm, I think "after" but with a hose, It probably doesn't matter. Just need to ensure its flowing clean because you don't want gunk in the engines cooling passages to block up the new rad, then fill it up with antifreeze mixture.

[Eagle]

Before, or during. The LAST thing you want to do is flush all the crappola from the block into a new radiator.