C175 Petroleum Engine Caterpillar

Jacket Water Aftercooling

Illustration 1	g06104372
(1) Active vents (2) Water-cooled turbos (3) Turbo water supply line (5) Radiator or heat exchanger (6) Electronic Thermostat (ESTAT) for the jacket water cooling system (7) Temperature Control Module (TCM) (8) Jacket Water Aftercooler (JWAC) (front aftercooler core) (9) Engine block (10) Jacket water pump (11) Engine oil cooler

Coolant is pulled from radiator or heat exchanger (5) to water pump (10). From the water pump, coolant is sent through engine oil cooler (11). From the engine oil cooler, the coolant is sent to engine block (9). From the engine block, coolant is sent to ESTAT (6) and to the jacket water passage of the aftercooler (8). From the JWAC the coolant is sent to turbo water supply line (3) and to the water-cooled turbos (2). The coolant from the turbos is sent to the radiator through an active vent line (1). The ESTAT regulates the amount of coolant that flows through the radiator or heat exchanger 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.

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 highest temperatures. As the coolant flows to the top of the cylinder liners, the coolant encounters a restriction due to smaller passages. The restriction causes the coolant flow to increase for improved cylinder 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 ESTAT and the after cooler core. Then the coolant is directed to the water-cooled turbo through the turbo water supply lines which removes the heat from the turbos, from which it is routed to the radiator through the active vent lines. Due to the restriction of the piping and after cooler core, a larger portion of the coolant flows to the ESTAT. The return coolant from the core is piped into a tee at the ESTAT.

Illustration 2	g06104429
(12) Three-way valve (13) Electronic Fluid Temperature Control (EFTC) (14) Stepper motor

The ESTAT utilizes a 3-way valve (12) that is electronically controlled by EFTC (13) to distribute the flow of the engine coolant. Engine temperate is inlet sensed by the engine jacket water pump outlet temperature sensor and outlet regulated by the EFTC to the radiator / heat exchanger. The outlet flow of coolant is directed by a piston that rides on a lead screw, which is driven by a stepper motor (14). For a cold engine, the EFTC bypasses the radiator/heat exchanger by sending the coolant directly back to the inlet of the water pump. As the engine warms, the EFTC controls the three-way valve to direct the correct amount of engine coolant through the radiator for cooling

The engine Electronic Control Module (ECM) transmits a temperature set point for the engine to the EFTC over the J1939 data link. The Engine Coolant Pump Outlet Temperature Sensor is used by the EFTC to detect the engine coolant temperature. The EFTC and three-way valve provides for complete control of coolant flow for accurate engine temperature.

Illustration 3	g06104443
(15) Engine Coolant Pump Outlet Temperature Sensor

JW Pump Outlet Temperature sensor connects to the EFTC and is powered by 3 VDC.

The ESTAT provides self-diagnostic functions and increased service reliability. These features can help to reduce the repair times and warranty claims that are associated with the cooling system.

There are two modes of operation and several states of operation for the EFTC.

The two modes of operation are the Position Control Mode and the Temperature Control Mode.

In the Position Control Mode the engine ECM overrides the EFTC via the Local CAN bus and commands the EFTC to drive the piston to a specific position. When in this mode, ET will report the Engine Coolant Thermostat Mode as "Position Control Mode" and the Engine Coolant Temperature Control State as "Active".

An example of Position Control Mode is the purge cycle. The purge cycle is used to pass any air trapped in the cooling system to the radiator top tank/expansion tank to prevent cavitation of the JW pump. This cycle will be initiated when the engine is first started. While this cycle is being performed, ET will report the Control Mode as "Position Control Mode" and the Control State as "Active". During the purge cycle the EFTC will position the piston at 20% for the first 100 seconds and then move the piston to 0% during the Purge Cycle. The Purge Cycle will terminate after 130 seconds or when the Engine Coolant Pump Outlet Temperature reads greater than 75° C (167° F).

Note: Refer to Troubleshooting, "Configuration Parameters" for default settings and ranges.

In the Temperature Control Mode the EFTC uses the Configuration Data, input from the Engine ECM via the Local CAN Bus, and input from the Engine Coolant Pump Outlet Temperature Sensor to determine the control state and the position of the piston. When in this mode, the EFTC is determining the position of the piston in the three-way valve and ET will report the Engine Coolant Thermostat Mode as "Temperature Control Mode".

When in the Temperature Control Mode the operating conditions of the engine will dictate the state of operation for the EFTC. The cooling system is allowed to change states when all the conditions for the desired state are achieved. The different states of the electronic fluid temperature control are described below:

Power-up – At power-up the EFTC assumes that the position of the piston is at the 100% position (fully open). It will then drive the piston in the counterclockwise (CCW) direction towards the 0% Position (fully closed). After 46 rotations of the stepper motor the piston will be guaranteed to be at the 0% Position, if all components are fully functional.

If the piston reaches the 0% position before the 46 rotations of the stepper motor are complete, the EFTC will continue to drive the stepper motor in the CCW direction. This action will create a ratcheting sound and is normal.

After the 46 rotations of the stepper motor are complete, the EFTC will exit "position control mode" (ECM is overriding position) and enters "temperature control mode" (ESTAT is self-controlling to the setpoint in the ADEM).

After this action, the inputs and Configuration Parameters will determine the modes and states the EFTC will operate in.

Active - When the Engine ECM is commanding the EFTC in the Position Control Mode the Control State of the EFTC will be Active.

Ambient – The control state will be ambient when the cooling system is nominally at the same temperature as the surrounding environment and the EFTC is in the Temperature Control Mode. The EFTC will enter this state when first powered up or when the cool down state has completed or when the engine is running and the temperature falls below the Coolant System Ambient Mode Temperature Threshold −5° C (-9° F). While in this state the EFTC will command the three-way valve to the 0% position. The EFTC will exit this state when power is removed or the temperature rises above the Coolant System Ambient Mode Temperature Threshold.

Warmup – The control state will be warmup when the engine is rejecting heat and the cooling system is operating at a temperature that is below the temperature that is necessary for operation of the valve in closed loop mode, and the EFTC is in the Temperature Control Mode. The EFTC will enter this state when the engine is running and the temperature rises above the Coolant System Ambient Mode Temperature Threshold. While in this state the EFTC will command the three-way valve to the 0% position. The EFTC will exit this state when the engine stops running or the temperature falls below the Coolant System Ambient Mode Temperature Threshold -5° C (-9° F) or the temperature rises above the Coolant System Regulating Mode Temperature Threshold.

This valve position recirculates all the coolant to the inlet of the engine.

Regulating – The control state will be regulating when the engine has warmed up enough to allow regulation of the coolant temperature to the desired set point. The EFTC will enter this state when the engine is running and the temperature rises above the Coolant System Regulating Mode Temperature Threshold. While in this state, the EFTC will adjust the position of the piston in the three-way valve to maintain the desired temperature. The EFTC will exit this state when the engine stops running or the temperature falls below the Coolant System Regulating Mode Temperature Threshold -5° C (-9° F).

Cool down – The control state will be cool down when the engine is stopped, the engine has partially cooled, and the EFTC is in the Temperature Control Mode. In this state the EFTC will set the piston in the three-way valve to a position that will allow the engine coolant to cool to the ambient temperature. The EFTC will enter this state when the engine is stopped and the temperature falls below the Coolant System Regulating Mode Temperature Threshold -5° C (-9° F) or the Engine Coolant Temperature System Cool down Mode Maximum Delay Time expires. While in this state the EFTC will command the three-way valve to the Coolant System Cool down Thermostat Opening. The EFTC will exit this state and enter the Ambient State when the Engine Coolant Block Inlet temperature falls below the Coolant System Ambient Mode Temperature Threshold temperature -5° C (-9° F), or if the engine starts running, or if the Engine Coolant Temperature System Cool down Mode Maximum Delay Time expires.

Note: The Cooldown State will only be active if the keyswitch input can be switched from B+ to open while the EFTC remains powered. Consult the electrical schematic for the specific application.

If the engine coolant pump outlet temperature sensor fails, the piston position will be overridden by the EFTC. Under this condition the EFTC will control the piston to 95% position. This piston position provides full cooling to allow the engine to continue running.

Note: If the engine is operated with a failed engine coolant pump outlet temperature sensor, the engine may be overcooled. The engine should be removed from service and repaired immediately.

If the engine is operated with a failed local CAN data link, the EFTC will operate in the Temperature Control Mode and will regulate to the engine coolant temperature set point entered into the EFTC Configurations as desired Engine Coolant Temperature Configuration.

Protection steps - The protection steps (ratcheting to the close position) takes place every 120 seconds when the following conditions are met:

● Control state is Warmup or Regulating

● Coolant Pump Outlet Temperature is less than Desired Engine Coolant Temperature Configuration.

Note: The above conditions will normally have the piston in the 0% position. These steps are taken to insure that the piston is really at the 0% position.

Separate Circuit Aftercooling

Illustration 4	g06104454
(16) External radiator or heat exchanger (17) Separate circuit aftercooler (SCAC) (rear aftercooler core) (18) SCAC water pump

Coolant flows to SCAC water pump (18) from an external radiator or heat exchanger (16). The coolant flows through rear aftercooler core (17) 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.