Originally Posted by ZAHANMA
Did you add a second pump inline to increase the flow through the system? If so, you may be pushing the coolant too fast through the system and not giving it ample time to be cooled by the air.
...alternatively, if you aren't pushing it fast enough now with the extra volume and twists and turns...the coolant could not be making it through the engine faast enough to cool it.
You have to have sufficient flow to make the water turbulent, insufficient flow has the water traveling in a laminar flow.
Turbulent flow has the water sweeping away the layer of water that is slowed by friction that sits against the side walls, these sidewalls are those that are in the cooled or the heated parts of the system. The sidewall layer effectively insulates the inner flowing coolant. The turbulent flow has all the coolant sweeping the sidewall thereby increasing the efficiency of the heat exchange. That means the coolant will pick up more heat and give up its heat faster.
Adding more surfaces, restrictions and bends will slow down the flow as friction and pressure losses increase.
Vane type pumps fall of in the volume moved as the back pressure increases.
You have to maintain the Reynolds number for turbulent flow. I have forgotten most of this but here is the Wiki on it.
Reynolds number - Wikipedia, the free encyclopedia