Engine Coolant Circuit Flow

When the engine is running, the coolant is circulated around the engine cooling system by the coolant pump. From the coolant pump, engine coolant flows through the cylinder heads and the engine oil cooler into the cylinder block and the heater manifold.

In the cylinder block, the coolant flows towards to the engine coolant outlet pipe. When the engine coolant is cold the thermostatic control valve remains closed and blocks engine coolant flow from the cylinder block to the electric thermostat. During the warm up phase the engine coolant flows to the heater manifold if an engine coolant bypass pipe.

After the engine coolant reaches the desired temperature, the thermostatic control valve opens and directs engine coolant towards the electric thermostat. During engine coolant warm up the thermostat is closed and the coolant flows direct from the engine coolant outlet pipe back to the coolant pump. When the coolant reaches operating temperature the electric thermostat begins to open, to regulate system temperature, and engine coolant flows from the engine coolant outlet pipe to the coolant pump if the radiator. When the thermostat is open, the coolant flow through the radiator also generates a coolant flow through the Automatic Transmission Fluid (ATF) cooler.

From the heater manifold the engine coolant flows through the electric throttle and the heater core, in parallel circuits that are unaffected by the position of the electric thermostat. From the electric throttle, the engine coolant merges with bleed coolant from the coolant pump and the engine coolant outlet pipe and flows to the coolant expansion tank. From the heater core, the engine coolant flows back to the inlet of the coolant pump.

Expansion and contraction of the engine coolant is accommodated by an air space in the coolant expansion tank and the compliance of the flexible hoses.