Yes, but then you lose performance as you get flow over the top of the block.

Don't get me wrong here, it works with weaker pumps just fine, its just better with one with good head pressure.

Im actually running mine at the moment purely using convection with a quad at 3GHZ (9650) and once the water starts to convect load temps were mid to high 30's under Linpack. Water in the res was 20C and CPU idled around 29 to 32C.

Who needs a pump LOL

I am going to rebuild the workbench to promote convection flow to 4 blocks for 4 boards and just use the pumps to cool the water in the reservoir, and then only when the water temp rises to high.