How is the cooler mounted - horizontally or vertically? If it's vertically mounted, then both the supply and return could be easily vented at their highest point. If it's a horizontal mount, then you really have to make sure you blow down both sides of the circuit (and that you have the valving in place to do so), or else you have the potential for getting vapor pockets in the loop. Plan 23's are best suited for hot water applications in my opinion; I have seen too many instances where process plan 23's lead to issues with coolers plugging, etc. That said, some do have success with them and swear by them. You will need to do whatever you can to maximize the circulation out of that inner pumping ring to be sure you are meeting the cooling and lubrication requirements of the inboard seal.