Car blows white smoke out of exhaust with warm temperature outside

Smell antifreeze in exhaust. Car runs smoothly but has overheated. My friend brought me his car to fix. He claims 2 dealers pressure tested it and he was told a head gasket was the problem. My buddies think it may be the intake manifold gasket. Is there a way to know which to fix? If I see the intake gasket is bad shall I stop there or replace the head gaskets also? He said one dealer replaced the thermostat and flushed the radiator but that did not fix the problem. Also, there is no indication of any coolant in the motor oil. Thanks