Pumping downwards?
 

Have some nagging suspicion about pumps placed on a high point, eg on top of a case inside a rad box, that the pump would have to suck real hard and hence it wouldn't be as good as placing it on the case "floor". Can anyone clarify?

thats why the res would have to be on top with the pump ;)

cant see how in a closed loop system, that it matters at all....

Pumps don't "suck" at least not most of the ones used here. They use an impellor and THROW the water out of the side outlet. - The negative pressure this creates is negliable, that is why most pumps you have to prime them.

Some Impellor pump work better with their inlet at the top so gravity helps into forcing the water into the mechanism but on a closed loop it doesn't really matter where your pump is or what posistion.

~ Boli

True. The only reason for putting a pump at the bottom in a closed loop is to prevent air bubbles from taking up residence in the pump.