MBE 900 – Section 15.15 High Engine Coolant Temperature

Section 15.15
High Engine Coolant Temperature

There are several causes for high engine coolant temperature. These probable causes are:‪

• Improper Engine Coolant Level
• Insufficient Radiator Air Circulation
• Faulty Pressure Control Cap
• Defective Coolant Hoses
• Incorrectly Adjusted Fan Belt
• Inoperative Thermo-Modulated Fan
• Faulty Thermostats
• Faulty Water Pump
• Combustion Gases in Coolant
• Abnormal Radiator Coolant Flow

Section 15.15.1
Troubleshooting Procedure for Improper Engine Coolant Level

To determine if improper engine coolant level is causing high engine coolant temperature, visually inspect the radiator coolant level; refer to OEM guidelines.‪

1. If the radiator coolant level is within approximately 50 mm (2.0 in.) of the radiator filler neck, check for insufficient radiator air circulation; refer to "15.15.3 Troubleshooting Procedure for Insufficient Radiator Air Circulation" .
2. If the radiator coolant level is not within approximately 50 mm (2.0 in.) of the radiator filler neck, refer to "15.15.2 Improper Coolant Level Resolution" .

Section 15.15.2
Improper Coolant Level Resolution

Perform the following steps to resolve improper coolant level:‪

1. Fill coolant system to correct level; refer to "4.1.1 Coolant Pre-Heater Removal" .
2. Verify coolant level resolution; refer to "15.15.2.1 Test Engine with Proper Coolant Level" .

Section 15.15.2.1
Test Engine with Proper Coolant Level

Perform the following to determine if proper coolant level resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check for insufficient radiator air circulation; refer to "15.15.3 Troubleshooting Procedure for Insufficient Radiator Air Circulation" .

Section 15.15.3
Troubleshooting Procedure for Insufficient Radiator Air Circulation

To determine if insufficient radiator air circulation is causing high engine coolant temperature, visually examine the radiator and radiator shrouding.‪

1. If the radiator is absent of clogging, debris, and dirt, check the pressure control cap; refer to "15.15.6 Troubleshooting Procedure for Faulty Pressure Control Cap" .
2. If the radiator has excessive clogging, debris, or dirt, refer to "15.15.4 Exterior Radiator Repair" .
3. If the radiator shrouding is not damaged, incorrectly positioned, or inadequate, check the pressure control cap; refer to "15.15.6 Troubleshooting Procedure for Faulty Pressure Control Cap" .
4. If the radiator shrouding is damaged, incorrectly positioned, or inadequate, refer to "15.15.5 Radiator Shroud Repair" .

Section 15.15.4
Exterior Radiator Repair

Perform the following for exterior radiator repair:‪

1. Clean the exterior radiator of all clogging, debris, or excessive dirt; refer to OEM guidelines.
2. Verify exterior radiator repair; refer to "15.15.5.1 Test Engine with Repaired Exterior Radiator and Shrouding" .

Section 15.15.5
Radiator Shroud Repair

Perform the following for radiator shroud repair:‪

1. Repair or replace damaged radiator shrouding; refer to OEM guidelines.
2. Verify exterior radiator repair; refer to "15.15.5.1 Test Engine with Repaired Exterior Radiator and Shrouding" .

Section 15.15.5.1
Test Engine with Repaired Exterior Radiator and Shrouding

Perform the following to determine if exterior radiator and shrouding repair resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check the pressure control cap; refer to "15.15.6 Troubleshooting Procedure for Faulty Pressure Control Cap" .

Section 15.15.6
Troubleshooting Procedure for Faulty Pressure Control Cap

To determine if a faulty pressure control cap is causing high engine coolant temperature, perform coolant pressure control cap tests.‪

1. If the cooling system pressure is less than or equal to 62 kPa (9 psi), check the coolant hoses; refer to "15.15.8 Troubleshooting Procedure for Defective Coolant Hoses" .
2. If the cooling system pressure is greater than 62 kPa (9 psi), refer to "15.15.7 Pressure Control Cap Resolution" .

Section 15.15.7
Pressure Control Cap Resolution

Perform the following steps to resolve faulty pressure control cap:‪

1. Remove and replace pressure control cap; refer to OEM guidelines.
2. Install a new pressure control cap; refer to OEM guidelines.
3. Verify pressure control cap repair; refer to "15.15.7.1 Test Engine with Replaced Pressure Control Cap" .

Section 15.15.7.1
Test Engine with Replaced Pressure Control Cap

Perform the following to determine if exterior radiator repair resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is normal, no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not normal, shut down the engine. Check coolant hoses; refer to "15.15.8 Troubleshooting Procedure for Defective Coolant Hoses" .

Section 15.15.8
Troubleshooting Procedure for Defective Coolant Hoses

To determine if defective coolant hoses are causing high engine coolant temperature, visually examine cooling system hoses; refer to OEM guidelines.‪

1. If cooling system hoses are not soft, deteriorated, collapsed, or have leaking connections, check the fan belts; refer to "15.15.10 Troubleshooting Procedure for Incorrectly Adjusted Fan Belt" .
2. If cooling system hoses are soft, deteriorated, collapsed, or have leaking connections, refer to "15.15.9 Coolant System Hoses Replacement" .

Section 15.15.9
Coolant System Hoses Replacement

Perform the following steps to resolve worn or damaged coolant system hoses:‪

1. Remove and replace damaged or worn coolant hoses as necessary; refer to OEM guidelines.
2. Install new coolant hoses as necessary; refer to OEM guidelines.
3. Verify replaced coolant system hoses; refer to "15.15.9.1 Test Engine with Replaced Coolant Hoses" .

Section 15.15.9.1
Test Engine with Replaced Coolant Hoses

Perform the following to determine if the new coolant hoses resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range, and visually examine replaced hoses for any leaks.
   1. If the engine coolant temperature is 82-105°C (180-221°F) and no leaks are found, no further troubleshooting is required.
   2. If the engine coolant temperature is 82-105°C (180-221°F) and leaks are found, repair the leaks; refer to "15.15.9 Coolant System Hoses Replacement" . Shut down the engine.
   3. If the engine coolant temperature is not 82-105°C (180-221°F) and no leaks are found, shut down the engine. Check fan belt; refer to "15.15.10 Troubleshooting Procedure for Incorrectly Adjusted Fan Belt" .

Section 15.15.10
Troubleshooting Procedure for Incorrectly Adjusted Fan Belt

To determine is a misadjusted fan belt is causing high engine coolant temperature, perform the following steps:‪

1. Check the auto tensioner for spring loading.
2. Compare tension to belt specifications.
   1. If the belt tension is normal, check the thermo-modulated fan; refer to "15.15.12 Troubleshooting Procedure for Inoperative Thermo-Modulated Fan" .
   2. If the belt tension is not normal, refer to "15.15.11 Belt Tension Resolution" .

Section 15.15.11
Belt Tension Resolution

Perform the following steps to resolve incorrect belt tension:‪

1. Replace the auto tensioner as required.
2. Verify belt tension resolution; refer to "15.15.11.1 Test Engine with Correct Belt Tension" .

Section 15.15.11.1
Test Engine with Correct Belt Tension

Perform the following to determine if belt tension resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check thermo-modulated fan; refer to "15.15.12 Troubleshooting Procedure for Inoperative Thermo-Modulated Fan" .

Section 15.15.12
Troubleshooting Procedure for Inoperative Thermo-Modulated Fan

To determine if an inoperative thermo-modulated fan is causing high engine coolant temperature, test the thermo-modulated fan. Refer to OEM guidelines.‪

1. If the thermo-modulated fan is functioning correctly, check thermostats; refer to "15.15.14 Troubleshooting Procedures for Faulty Thermostats" .
2. If the thermo-modulated fan is not functioning correctly, refer to "15.15.13 Thermo-Modulated Fan Replacement" .

Section 15.15.13
Thermo-Modulated Fan Replacement

Perform the following steps to replace inoperative thermo-modulated fan:‪

1. Replace inoperative thermo-modulated fan; refer to OEM guidelines.
2. Verify thermo-modulated fan replacement; refer to "15.15.13.1 Test Engine with Replaced Thermo-Modulated Fan" .

Section 15.15.13.1
Test Engine with Replaced Thermo-Modulated Fan

Perform the following steps to determine if thermo-modulated fan replacement resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check thermostats; refer to "15.15.14 Troubleshooting Procedures for Faulty Thermostats" .

Section 15.15.14
Troubleshooting Procedures for Faulty Thermostats

To determine if faulty thermostats are causing high engine coolant temperature, perform the following:‪

1. Remove thermostat from the thermostat housing; refer to "4.6.1 Thermostat Removal" .
2. Inspect thermostat for correct operation; refer to "4.6.1.1 Thermostat Checking" .
   1. If thermostat is fully open at 95°C (203°F), check water pump; refer to "15.15.16 Troubleshooting Procedure for Faulty Water Pump" .
   2. If thermostat is not fully open at 95°C (203°F), refer to "15.15.15 Thermostat Replacement" .

Section 15.15.15
Thermostat Replacement

Perform the following steps to replace thermostats:‪

1. Install new thermostat; refer to "4.6.2 Thermostat Installation" .
2. Verify replaced thermostat; refer to "15.15.15.1 Test Engine with New Thermostat" .

Section 15.15.15.1
Test Engine with New Thermostat

Perform the following steps to determine if thermostat replacement resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check water pump; refer to "15.15.16 Troubleshooting Procedure for Faulty Water Pump" .

Section 15.15.16
Troubleshooting Procedure for Faulty Water Pump

To determine if a faulty water pump is causing high engine coolant temperature, perform the following:‪

1. Remove the water pump and inspect pump for failed shaft or rotor. For Non-EGR engines refer to "4.2.1 Coolant Pump Removal" ; for EGR engines refer to "4.2.1 Coolant Pump Removal" .
2. Replace water pump if damaged. For Non-EGR engines refer to "4.2.2 Coolant Pump Installation" ; for EGR engines refer to "4.3.2 Coolant Pump Installation – EGR Engine" .

Section 15.15.16.1
Test Engine with Replaced Water Pump

Perform the following steps to determine if thermo-modulated fan replacement resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check combustion gases in coolant; refer to "15.15.17 Troubleshooting Procedure for Combustion Gases in Coolant" .

Section 15.15.17
Troubleshooting Procedure for Combustion Gases in Coolant

To determine if combustion gases in coolant is causing high engine coolant temperature, perform a cylinder compression test. Refer to "1.2.2.2 Compression Testing" .‪

1. If test results are to specifications; check radiator coolant flow; refer to "15.15.19 Troubleshooting Procedure for Abnormal Radiator Coolant Flow" .
2. If test results are not to specifications, refer to "15.15.18 Cylinder Head Gasket Replacement" .

Section 15.15.18
Cylinder Head Gasket Replacement

Perform the following steps to replace cylinder head gasket:‪

1. Remove and replace cylinder head gasket; refer to "1.2.2 Cylinder Head Installation" .
2. Verify new cylinder head gasket replacement; refer to "15.15.18.1 Test Engine with Replaced Cylinder Head Gasket" .

Section 15.15.18.1
Test Engine with Replaced Cylinder Head Gasket

Perform the following to determine if cylinder head gasket replacement resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Check radiator coolant flow; refer to "15.15.19 Troubleshooting Procedure for Abnormal Radiator Coolant Flow" .

Section 15.15.19
Troubleshooting Procedure for Abnormal Radiator Coolant Flow

To determine if abnormal radiator coolant flow is causing high engine coolant temperature, perform the following:‪

1. Install a sight glass with string (both ends) to the radiator outlet hose near radiator and before fill and heater return lines; see Figure "Radiator Flow Check" .
   

   Figure 1. Radiator Flow Check

   PERSONAL INJURY ‪
   To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

2. Start and run the engine at full load.
3. Observe the string for flow and direction as well as the fill and bleed lines. Continue observation while varying the engine speed between 1800-2400 rpm.
   1. If a balanced coolant flow is observed in the sight glass, call Detroit Diesel Customer Support Center at 313-592-5800. Shut down the engine.
   2. If a balanced coolant flow is not observed in the sight glass, refer to "15.15.20 Abnormal Radiator Coolant Flow Resolution" . Shut down the engine.

Section 15.15.20
Abnormal Radiator Coolant Flow Resolution

Perform the following steps, as necessary, to resolve abnormal radiator coolant flow:‪

1. Correct bleed line size; refer to OEM guidelines.
2. Correct fill line size or connector fitting size; refer to OEM guidelines.
3. Correct restrictive top tank opening; refer to OEM guidelines.
4. Correct location of standpipe; refer to OEM guidelines.
5. Verify repairs made to correct abnormal radiator coolant flow; refer to "15.15.20.1 Test Engine with Resolved Radiator Coolant Flow" .

Section 15.15.20.1
Test Engine with Resolved Radiator Coolant Flow

Perform the following to determine if abnormal radiator coolant flow repair resolved high engine coolant temperature:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine through its operating range with no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
   1. If the engine coolant temperature is 82-105°C (180-221°F), no further troubleshooting is required. Shut down the engine.
   2. If the engine coolant temperature is not 82-105°C (180-221°F), shut down the engine. Call the Detroit Diesel Customer Support Center at 313-592-5800.