[snj1013]

Wow, all sorts of replies, and about 90% of them are ignoring the fact that the OP has combustion gases entering into the coolant. I would get another set of head gaskets and give it another go. Perhaps add a bunch of fans to keep the engine cool while breaking in, but focus in on fixing the head gasket leak before fixing anything else.

 

[snj1013]

Which came first, the chicken or the egg ?

Simply put, Overheating is the #1 cause of head gasket failure.

So overheating IS what needs to be addressed #1 . Of course a new head gasket is in order. But it will fail too if the overheating issue is not resolved firstly

Z

Fair point, but I am assuming the head gasket/head was not installed properly and likely leaking from the moment the OP started the engine and thus the reason for his very rapid overheating condition. Based on the fact that the engine is freshly rebuilt, and how quickly the engine started to overheat, I would not assume I have a cooling issue, but I would assume I have an issue with the rebuild.