Water bypass on FE427

[Eljaro]

I just fired up my 427 top oiler after a mayor engine rebuilt, which included a reground crankshaft with new crankshaft and rod bearings , new Comp cam 282H with springs. I have a set of Dove F5 heads which worked fine before , and I did hardly ever see temperatures over 195ºF while driving.
While running the engine in at about 2000 rpm for about 15 minutes the engine got very hot (water at 230º)
I did only change one thing from the previous setup , which is the installation of the bypass which goes from the intake manifold to the water pump. It was plugged before and I suspect this is causing the overheating . What is this bypass good for, why did the engine builder before me plug this bypass?. Any hints?

[Brent Mills]

I'm definately not the expert, but during run in, I believe there's more friction, and well, more heat. Furthermore, sitting at a stand still, at 2k rpms might be a little more than your electric fan can handle? During run in, I had a garden hose so when the temp started to rise above my thermostat 185, I just set the hose on it for a minute and kept her pretty stable around 185/190.

As for the bypass, mine is not blocked.

[Eljaro]

You might be right , Brent, but the engine has no new pistons, which is what generates most of the run in heat. It could well be that the fan does not cope with heat generated at 2000rpm during 15 min. at standstill. The air temp here is about 34ºC right now, quite hot.
I will take a ride tomorrow and see what happens with the temp while in motion.
Anyway, I still would like to know what the bypass really does and why someone may want to plug it.