Jacket Water Aftercooling
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| Illustration 1 | g02373480 |
(1) Radiator or heat exchanger (2) Electronic thermostat for the jacket water cooling system (3) Temperature Control Module (TCM) (4) Engine block (5) Jacket Water Aftercooler (JWAC) (front aftercooler core) (6) Jacket water pump (7) Engine oil cooler | |
Coolant is pulled from radiator (1) to water pump (6). From the water pump, coolant is sent through engine oil cooler (7). From the engine oil cooler, the coolant is sent to engine block (4). From the engine block, part of the coolant is sent to electronic thermostat (2) while the remainder is sent to JWAC (5). The coolant from the JWAC is returned to the electronic thermostat. The electronic thermostat regulates the amount of coolant that flows through the radiator in order to control engine temperature. The engine coolant that does not flow through the radiator is bypassed directly to the inlet of the jacket water pump.
The coolant flows from the engine oil cooler into the water jacket at the front of the engine block. The coolant is directed toward the rear of the block through distribution manifolds. The distribution manifolds distribute the coolant to the water jacket for each cylinder. The coolant flows upward through the water jackets and around the cylinder liners. This area has the hottest temperatures. As the coolant flows to the top of the cylinder liners, the area of the water passages becomes smaller. This smaller area causes the coolant flow to increase for better liner cooling. Coolant flows from the top of the liners into passages that are cast into each of the cylinder heads. The coolant flows from the cylinder head back into the block and is returned to the front of the engine.
As the coolant exits the front of the engine block, the coolant is directed through piping to the electronic thermostat and the JWAC aftercooler core. Due to the restriction of the piping and aftercooler core, a larger portion of the coolant flows to the electronic thermostat. The return coolant from the core is piped into a tee at the electronic thermostat.
The electronic thermostat utilizes a 3-way valve that is electronically controlled by TCM (3) to distribute the flow of the engine coolant. For a cold engine, the TCM bypasses the engine block by sending the coolant directly back to the inlet of the water pump. As the engine warms, the TCM controls the electronic thermostat to direct the correct amount of engine coolant through the radiator for cooling.
The Electronic Control Module (ECM) transmits a temperature setpoint for the engine to the TCM over the J1939 data link. A coolant temperature sensor is used by the TCM to detect the engine coolant temperature. The TCM and electronic thermostat provides for complete control of coolant flow for accurate engine temperature.
The TCM commands a cooling purge cycle during engine start-up that removes trapped air from the cooling system. For the first 100 seconds after engine start-up, the TCM partially opens the 3-way valve to allow coolant flow through the radiator. As coolant flows through the radiator, the coolant flow slows to allow aeration within the coolant to escape to the top of the radiator tank.
The correct operation of the electronic thermostat during the purge cycle can be confirmed by observing the main shaft extension for the 3-way valve. To observe the operation of the electronic thermostat, perform the following procedure:
- Remove electrical power from the ECM.
- Remove the cover (9) from the end of the 3-way valve. Locate main shaft extension (8) .
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| Illustration 2 | g03348455 |
Location of the main shaft extension for the 3-way valve (8) Main shaft extension (9) Cover | |
- Restore the electrical power to the ECM. Observe the rotation of the main shaft extension for the 3-way valve.
During the powerup sequence, the shaft extension will rotate clockwise while the valve travels to the end stop of the valve. Listen for the piston to hammer the end stop in order to establish the valve position.
- Start the engine. Observe the main shaft extension for the 3-way valve.
When the engine is started, the main shaft extension will rotate clockwise to a partially open position. The shaft will rotate clockwise for approximately 30 seconds in order to purge the air out of the system. The shaft will then rotate slowly counterclockwise to the closed position. The duration of the entire purge cycle is approximately 100 seconds.
- Shut down the engine and replace the cover. Tighten the bolts.
If the purge cycle completes successfully, place the engine into service.
If a problem is discovered during the procedure, perform the necessary repairs. Refer to Troubleshooting, "Coolant Temperature Control Module - Test" for troubleshooting information.
Also, when a hot engine is shut down, the TCM will continue to control the electronic thermostat valve until the coolant temperature reaches approximately 50° C (122° F). When the coolant temperature drops below 50° C (122° F), the 3-way valve is controlled to the bypass position. If the coolant temperature is below 50° C (122° F) during engine shutdown, the valve is commanded directly to the bypass position.
Separate Circuit Aftercooling
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| Illustration 3 | g02374217 |
(10) External radiator or heat exchanger (11) Separate circuit aftercooler (SCAC) (rear aftercooler core) (12) SCAC water pump | |
Coolant flows to SCAC water pump (12) from an external radiator or heat exchanger (10). The coolant flows through rear aftercooler core (11) and returns to a thermostatic valve that controls the bypass coolant flow. When the thermostatic valve is closed, the coolant is sent back to the inlet of the separate circuit water pump. As the temperature of the coolant increases, the thermostatic valve opens. When the thermostatic valve is open, the coolant flow in the bypass line is restricted. The coolant is diverted to the external radiator or heat exchanger.