Pinpoint Test B: The Engine Overheats
Engine Cooling
Pinpoint Test B: The Engine Overheats
Normal Operation
The engine cooling system maintains the engine temperature 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. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump, operated by engine rotation through a pulley driven by the accessory drive belt circulates 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 flows through the radiator circuit 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.
This pinpoint test is intended to diagnose the following:
- Low coolant level
- External engine coolant leak
- Airlock in system
- Pressure relief cap installation
- Restricted airflow through the A/C condenser/radiator
- Internal engine coolant leak
- Coolant condition/concentration
- Accessory drive components
- Non-OEM engine enhancement components
- Electric cooling fan
- Radiator
- Thermostat
- Engine Coolant Temperature (ECT)
- ECT (Engine Coolant Temperature) gauge
- Coolant pump
- Coolant flow restriction
PINPOINT TEST B : THE ENGINE OVERHEATS
WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.
B1 CARRY OUT INSPECTION AND VERIFICATION
- Carry out the Inspection and Verification procedure Inspection and Verification.
Were any concerns found?
Yes
REPAIR as needed. TEST the system for normal operation.
No
GO to B2.
B2 CHECK FOR AN AIRFLOW OBSTRUCTION
- Check the radiator or A/C condenser for an external obstruction such as leaves or cardboard.
Is an obstruction present?
Yes
REMOVE the obstruction. TEST the system for normal operation.
No
GO to B3.
B3 CHECK THE ENGINE COOLANT LEVEL
NOTE: Allow the engine to cool before checking the coolant level.
- Ignition OFF.
- Visually check the engine coolant level in the coolant expansion tank.
Is the engine coolant level within specification?
Yes
GO to B4.
No
ADJUST the engine coolant level as necessary. GO to B4.
B4 PRESSURE TEST THE ENGINE COOLING SYSTEM
- Pressure test the engine cooling system. Refer to Component Tests, Cooling System Pressure Test Component Tests and General Diagnostics.
Does the engine cooling system leak externally?
Yes
REPAIR or INSTALL new components. TEST the system for normal operation.
No
GO to B5.
B5 CHECK THE ENGINE COOLANT FOR AN INTERNAL LEAK
- Inspect the engine coolant in the coolant expansion tank for signs of engine oil.
Is engine oil evident in the coolant?
Yes
GO to Engine for engine diagnosis.
No
GO to B6.
B6 CHECK THE ENGINE OIL FOR COOLANT
- Remove the oil level indicator from the engine.
Is coolant evident in the oil?
Yes
GO to Engine for engine diagnosis.
No
GO to B7.
B7 CHECK THE COOLING SYSTEM FOR COMBUSTION GASES
- NOTE: Use UView(R) Combustion Leak Tester part number UVU560000-R or equivalent.
Using a cooling system combustion gas leak tester, following the instructions supplied with the tester, check the coolant for combustion gases.
Are combustion gases present?
Yes
GO to Engine for engine diagnosis.
No
GO to B8.
B8 CHECK COOLANT CONDITION
- Check the coolant for dirt, rust or contamination and check the coolant concentration.
Is the coolant condition OK?
Yes
GO to B9.
No
FLUSH the engine cooling system. REFER to Cooling System Flushing Cooling System Flushing. TEST the system for normal operation.
B9 CHECK THE ELECTRIC COOLING FAN OPERATION
- Start the engine.
- Place the climate control function selector in the MAX A/C position and the blower motor switch in the HI position.
Did the electric cooling fan operate?
Yes
GO to B10.
No
DIAGNOSE the electric cooling fan operation. REFER to Computers and Control Systems Information.
B10 CHECK THE COOLANT PUMP OPERATION
- Start the engine.
- Allow the engine to run for 30 minutes. Place the climate control function selector in the MAX HEAT position. Feel the heater outlet hose.
Is the heater outlet hose hot?
Yes
GO to B11.
No
INSTALL a new coolant pump. TEST the system for normal operation.
B11 CHECK THE THERMOSTAT OPERATION
- Start the engine.
- Allow the engine to run for 30 minutes. Feel the lower radiator hose.
Is the lower radiator hose hot?
Yes
CHECK the ECT (Engine Coolant Temperature) gauge operation.
No
GO to B12.
B12 VISUALLY INSPECT THE THERMOSTAT
- Carry out the Thermostat Visual Inspection in the Component Tests portion Component Tests and General Diagnostics.
Is the thermostat damaged?
Yes
INSTALL a new thermostat. TEST the system for normal operation.
No
INSTALL a new thermostat. TEST the system for normal operation. If the engine still overheats, INSTALL a new radiator. TEST the system for normal operation.