Engine Coolant Circuit Flow

The Powertrain Control Module (PCM) controls the variable coolant pump to give the minimum flow to support all cooling requests from the engine components. The variable coolant pump has a shroud inside that slides over the impeller to control the quantity of engine coolant pumped into the engine. The purpose is only to pump the minimum quantity of engine coolant necessary around the engine. This decreases the load on the engine and improves fuel consumption and emissions.

The variable coolant pump generates pressure with every rotation. A solenoid valve controls the coolant flow into either to the shroud assembly, or back to the engine cooling system.

The PCM controls the shroud solenoid in hardwired.

For additional information, refer to: ELECTRONIC ENGINE CONTROLS .

The flow modes of the variable coolant pump are the following:

NOTE: Flow percentages are approximate values.

0 = 0 flow
1 = 12% flow
2 = 25% flow
3 = 50% flow
4 = Full flow (Default position).

The PCM receives input signals from the following components to calculate the level of cooling required:

Cylinder head temperature sensor
Cylinder block temperature sensor
Ambient Air Temperature (AAT) sensor
Engine Coolant Temperature (ECT) sensor
Radiator outlet temperature sensor.

The control of engine coolant flow reduces engine load. The objective of this is to decrease fuel consumption and emissions in all operation conditions.

Any request from 0 - 100% flow can be fulfilled at most engine speeds, contributing to the whole engine thermal management strategy. The internal pressure within the variable coolant pump acts against a return spring in the housing. The solenoid is open without a signal from the PCM. Therefore the shroud returns to its base position under spring force, resulting in full flow from the variable coolant pump.

When the engine is running, the variable coolant pump circulates the engine coolant through the engine cooling system.

At engine start up, the shroud of the variable coolant pump is CLOSED. This prevents coolant flow in the cylinder block. When required, the PCM can request the opening of the variable coolant pump shroud to provide the required engine coolant flow.

When the engine coolant is cold, the wax thermostat is CLOSED and the engine coolant flows directly back to the variable coolant pump.

When the engine coolant reaches operating temperature, the electric thermostat begins to open. The engine coolant flows through both the bypass route and radiator system to provide the required engine cooling.

When the engine coolant temperature reaches 115°C (239°F), the wax thermostat is fully OPEN. The majority of the engine coolant passes through the radiator and the Automatic Transmission Fluid (ATF) cooler to the variable coolant pump. The engine coolant still passes through the turbocharger, heater core, electric throttle and oil cooler in proportion.

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.