944 Cooling System — Turbocharged
Overview of the turbocharged 944 cooling system, including thermostat operation, turbocharger cooling circuit with electric post-shutdown pump, turbo thermostat, and check valve.
The 944 Turbo cooling system bypasses the radiator until the coolant temperature reaches 83 °C, at which point the thermostat opens. After the thermostat opens, coolant is circulated through the radiator and back to the suction of the water pump.
Flow through the heater core is controlled by a vacuum-operated diaphragm valve that fails open on loss of vacuum. Vacuum is supplied to the valve operator via a vacuum solenoid in the HVAC system.
Turbocharger Cooling Circuit
With the engine shut down, if the temperature in the discharge cooling line from the turbocharger rises to 115 °C (as sensed by a temperature sensor), the electric turbocharger cooling pump activates to circulate coolant from the expansion tank, through the turbocharger, and back to the expansion tank. The turbocharger cooling pump also runs for 25 seconds any time the engine is shut off, regardless of discharge line temperature.
When the engine is running, a turbo thermostat opens at 82 °C. The water pump then draws coolant from the expansion tank through the non-running turbo cooling pump and through the turbocharger bearing housing. A check valve in the expansion tank prevents coolant from being drawn back from the turbocharger discharge line to the expansion tank — without this valve, flow would bypass the turbocharger.