Chevyart, do you run a thermosat or anything to slow down the water running thru the rad it might be going thru the rad to fast and not being cooled down before returning to the engine. What fan are you running. Timing to high or to low will also make an engine run hot. I have ran 400 blocks half filled and driven them on the road with no overheating. One thing you need to think about is you are running less water now that the block is filled. I ran lines from the water pump to the heads (not the block) to keep from having a hot spot between the two center cylinders. I only ran lines like that when running nitrous. I hope some of this will help as there is alot of things that can make an engine run hot.