Engine Cooling - System Operation and Component Description: Notes
System Diagram
| Item | Description |
|---|---|
| 1 | Reservoir |
| 2 | Heater core |
| 3 | Oil cooler |
| 4 | Thermostat housing - small/large coolant circuit and bypass valve |
| 5 | Cylinder head - exhaust side |
| 6 | Short block thermostat |
| 7 | Cylinder block and cylinder head - intake side |
| 8 | Mechanical coolant pump |
| 9 | Electric coolant pump |
| 10 | Turbocharger |
| 11 | Radiator |
System Operation
Cooling system function
The cooling system is controlled in 3 phases .
Phase 1
When the engine is cold , the small/large coolant circuit thermostat and the short block thermostat are closed.
The mechanical coolant pump delivers the coolant only to the exhaust-side part of the cylinder head. In this phase, the coolant in the coolant jacket around the cylinder and in the intake-side part of the cylinder head remains motionless.
Below a coolant temperature of approximately 70°C (158°F) and below an engine speed of approximately 3000 RPM, only the exhaust-side part of the cylinder head is cooled.
| Item | Description |
|---|---|
| 1 | Reservoir |
| 2 | Heater core |
| 3 | Oil cooler |
| 4 | Casing - Thermostat - Small/large coolant circuit and bypass valve |
| 5 | Cylinder head - exhaust side |
| 6 | Cylinder block thermostat |
| 7 | Cylinder block and cylinder head - intake side |
| 8 | Mechanical coolant pump |
| 9 | Electric coolant pump |
| 10 | Turbocharger |
| 11 | Radiator |
The coolant flows from the part of the cylinder head on the exhaust side into the thermostat housing in the small/large coolant circuit and bypass valve and, from there, via the heater core to the oil cooler and then back to the coolant pump.
In addition, part of the coolant flows from the short block through the electrical coolant pump and, from there, on past the exhaust gas turbocharger to the coolant expansion tank and then back to the coolant pump.
| Item | Description |
|---|---|
| 1 | Coolant flow from oil cooler |
| 2 | Coolant flow to heater core |
| 3 | Small/large coolant circuit thermostat |
| 4 | Bypass valve |
| 5 | Coolant flow to mechanical coolant pump |
| 6 | Coolant flow from exhaust-side part of the cylinder head |
Below a coolant temperature of approximately 70°C (158°F) and below an engine speed of approximately 3000 RPM, the small/large coolant circuit thermostat and the bypass valve are closed.
| Item | Description |
|---|---|
| 1 | Coolant flow from oil cooler |
| 2 | Coolant flow to heater core |
| 3 | Small/large coolant circuit thermostat |
| 4 | Bypass valve |
| 5 | Coolant flow to mechanical coolant pump |
| 6 | Excessive coolant flow from exhaust-side part of the cylinder head |
If the engine speed exceeds approximately 3000 RPM, the bypass valve opens. The now increased coolant pressure from the engine opens the bypass valve so that the increase pressure can escape directly to the intake side of the coolant pump.
Phase 2
The short block thermostat opens at a coolant temperature of 70 °C (158°F) and is completely open at 85 °C (185°F) .
As with a conventional system, this opens the small coolant circuit .
The coolant pump now delivers coolant to the cooling jackets and around the cylinders, and enters the entire cylinder head via the bore holes.
| Item | Description |
|---|---|
| 1 | Reservoir |
| 2 | Heater core |
| 3 | Oil cooler |
| 4 | Thermostat housing - small/large coolant circuit and bypass valve |
| 5 | Cylinder head - exhaust side |
| 6 | Cylinder block thermostat |
| 7 | Cylinder block and cylinder head - intake side |
| 8 | Mechanical coolant pump |
| 9 | Electric coolant pump |
| 10 | Turbocharger |
| 11 | Radiator |
Phase 3
| Item | Description |
|---|---|
| 3 | Small/large coolant circuit thermostat |
| 4 | Bypass valve |
| 7 | Coolant flow to the radiator |
The small/large coolant circuit thermostat opens at a coolant temperature of 92 °C (198°F) and is completely open at 106 °C (223°F) . At the same time, the bypass valve thermostat closes. This ensures that the entire coolant flow, regardless of the coolant pressure, is always routed via the radiator.
| Item | Description |
|---|---|
| 1 | Reservoir |
| 2 | Heater core |
| 3 | Oil cooler |
| 4 | Casing - Thermostat - Small/large coolant circuit and bypass valve |
| 5 | Cylinder head - exhaust side |
| 6 | Cylinder block thermostat |
| 7 | Cylinder block and cylinder head - intake side |
| 8 | Mechanical coolant pump |
| 9 | Electric coolant pump |
| 10 | Turbocharger |
| 11 | Radiator |