Anyone have any insight to this? I bought an 88' runner, 22re with a blown head gasket. I put in another engine i have that was running great. Also flushed the heater lines going in the firewall and the radiator. Just took it for a spin after the engine swap. It eventually overheated and steam built up above the defrost vent on the window. Also heard a hissing sound from the heater area.???

 

Sounds like a heater core leak, and maybe not all the air was purged from the cooling system as well.

 

+1^^^ for causing steam.
AND ....
Water pump, fan clutch (aka liquid coupling working), and thermostat all working?