Originally Posted by diehrd
When people say putting the rad after pump lowers temps I doubt there really thinking it through,because the idea although on the surface makes sense it leaves out a criticle factor.
The water is in constant motion,It never stops,and depends completly on motion to be effective.There is such a tiny measurable difference in water temp when water flows past cpu block to gpu block that it would take lab quality equipment to measure the increase.
You are saying that the water coming out of the radiator is the same temp as the water later in the loop? Maybe with a really bad radiator, but that is not ideal.
Perhaps I misunderstood, but the reason running the flow;
pump> rad> CPU> res> pump
is because the radiator will cool the water down right before it enters the block, which will then allow it to pick up more heat in the CPU block. Water can only absorb so much heat, same as any other material, and as it approaches it's maximum ability, it's efficency is reduced. Therefore, cooling the water as much as possible before entering the CPU block means that it can absorb more heat faster than water of a higher tempeture could.
You have a good point about length of tubing and bends, however, that does not change the fact that the ideal setup, and one that should be planned for, is pump to radiator first. Making that loop with minimal bends and tubing is a given, but it's still making that loop that yields the best temps.