I honestly have no clue on what coolant was in it. Remember I am dealing with a lot of unknowns. It will all be well known now that I have built it right.Blown head gasket from a cold start? And light driving I doubt it. Even if it was -40 c I couldn't see that as a factor for a head gasket. Maybe breaking a ring or scuffing a cylinder wall. What type of coolant was in it?