From Redmoe's post on page 4.
Phase 2:
During an initial start-up with an ambient temperature 60-75F (16-24C) or cooler (calibratable) the coolant shutoff solenoid valve remains open. This allows engine coolant to circulate through the heater core providing cabin heat to the customer. When the coolant shutoff solenoid valve is open, the coolant circulates through the engine (cylinder block and cylinder head), heater core, engine oil cooler, transmission oil cooler, turbo, and degas bottle. Coolant is also routed into the thermostat housing which initiates the warm-up phase of the thermostat.