Engine Cooling System: Overview Lincoln MKS I

Principles of Operation

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. From the coolant pump, coolant is sent through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core and turbochargers with coolant. The coolant pump is operated by engine rotation through a sprocket which is driven by the timing chain to circulate the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant is allowed to flow through the radiator circuit in order to transfer engine-generated heat to the outside air.

The degas bottle holds surplus coolant and removes air from the cooling system, which reduces hot spots. It also allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.

The cooling fan draws air through the radiator to help cool the system coolant as it passes through the radiator.

The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor will be executed once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 is set, and the Malfunction Indicator Lamp (MIL) will be illuminated.

For vehicle/engine specific information, refer to ENGINE COOLING .

Normal Operation

The engine cooling system is a closed system that provides for coolant expansion and contraction and also changes in pressure as coolant warms and cools with engine operation. Various gaskets, seals, hoses and clamps are used to contain coolant within the cooling system and keep other fluids and contaminants from entering the cooling system.

Coolant loss can be attributed to either external or internal leaks anywhere within the cooling system.

For vehicle/engine specific information, refer to ENGINE COOLING .

This pinpoint test is intended to diagnose the following

1. Coolant hoses or tubes
2. Hose clamps
3. Thermostat O-ring seal or gasket
4. Coolant pump O-ring seal or gasket
5. Thermostat housing
6. Radiator
7. Pressure relief cap
8. Coolant pump leaking from weep hole
9. Heater core
10. Engine gaskets
11. Degas bottle
12. Cylinder block core plugs
13. Cylinder head core plugs
14. Block heater (if equipped)
15. Turbochargers (if equipped)

The engine cooling system functions to maintain engine temperatures during operation. Correct coolant flow through the engine, radiator and remainder of cooling system passages and components is essential to maintaining a correct engine temperature.

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. From the coolant pump, coolant is sent through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump is operated by engine rotation through a sprocket which is driven by the timing chain to circulate the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant is allowed to flow through the radiator circuit in order to transfer engine-generated heat to the outside air.

Engine overheating generally occurs when there is a disruption in the ability to control either coolant flow at the correct rate, the inability to transfer heat from the engine through the coolant (including low coolant) or an inability to transfer engine-generated heat to the outside air through the radiator.

For vehicle/engine specific information, refer to ENGINE COOLING .

1. DTC P1285 (Cylinder Head Overtemperature Condition) - Indicates an engine overheat condition was sensed by the Cylinder Head Temperature (CHT) sensor.
2. DTC P1299 (Cylinder Head Overtemperature Protection Active) - Indicates an engine overheat condition was detected by the CHT sensor. A failure mode effects management strategy called failsafe cooling was activated to cool the engine.

This pinpoint test is intended to diagnose the following

1. Low coolant level
2. External engine coolant leak
3. Airlock in system
4. Pressure relief cap installation
5. Restricted airflow through the A/C condenser/radiator
6. Internal engine coolant leak
7. Coolant condition/concentration
8. Non-OEM engine enhancement components
9. Electric cooling fan
10. Engine Coolant Temperature (ECT) indicator system (gauge)
11. CHT sensor
12. Heater core
13. Coolant pump
14. Coolant flow restriction
15. Missing engine vent hose check valve or incorrect orientation of check valve

The engine cooling system functions to maintain engine temperatures during operation. Correct coolant flow through the engine, radiator and remainder of cooling system passages and components is essential to maintaining a correct engine temperature.

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. From the coolant pump, coolant is sent through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump is operated by engine rotation through a sprocket which is driven by the timing chain to circulate the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant is allowed to flow through the radiator circuit in order to transfer engine generated heat to the outside air.

Concerns of engine inability to reach normal operating temperature typically occur when the rate of coolant flow through some coolant circuits (radiator, heater core) is more than expected given the conditions, or when the electric cooling fans operate all the time. Heat is not allowed to build in the engine because a heat exchanger is removing too much heat, including the radiator, heater core and oil cooler. In addition, perceived concerns that the engine does not reach normal operating temperature can be related to a low coolant level or trapped air which does not allow for hot coolant to be available at the heater core, an inoperative climate control system, or for concerns perceived or related to an incorrect engine temperature gauge indication.

For vehicle/engine specific information, refer to ENGINE COOLING .

1. DTC P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control) - Indicates the Cylinder Head Temperature (CHT) sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting the engine.
2. DTC P0128 (Coolant Thermostat [Coolant Temp Below Thermostat Regulating Temperature]) - Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.

This pinpoint test is intended to diagnose the following

1. Low coolant level
2. Thermostat
3. Engine Coolant Temperature (ECT) indicator system (gauge)
4. Engine cooling fan