90304-ZW1-003 Honda SEE PART DETAILS - SUP; NUT, SELF-LOCK (M25X2.0) (Honda Code 4901021).

Illustration 1 g03676565
(1) Radiator or heat exchanger
(2) Electronic thermostat for the jacket water cooling system
(3) Engine block
(4) Jacket Water Aftercooler (JWAC) (front aftercooler core)
(5) Jacket water pump
(6) Engine oil cooler Coolant is pulled from radiator or heat exchanger (1) to water pump (5). From the water pump, coolant is sent through engine oil cooler (6). From the engine oil cooler, the coolant is sent to engine block (3). From the engine block, coolant is sent to electronic thermostat (2) and to the jacket water passage of the aftercooler (4). The coolant from the aftercooler is returned to the electronic thermostat. The electronic thermostat regulates the amount of coolant that flows through the radiator or heat exchanger 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.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 electronic thermostat and the after cooler core. Due to the restriction of the piping and after cooler 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.
Illustration 2 g03677762
(7) Three-way valve
(8) Electronic Fluid Temperature Control (EFTC)
(9) Stepper motor The electronic thermostat utilizes a 3-way valve (7) that is electronically controlled by EFTC (8) 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 (9). 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 coolingThe 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 g03687890
(10) Engine Coolant Pump Outlet Temperature Sensor JW Pump Outlet Temperature sensor connects to the EFTC and is powered by 3 VDC.
Table 1
Valve Position Water Flow
0% Position Block Outlet to JW Pump Inlet
100% Position Block Outlet to Radiator Top Tank/Expansion Tank 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.
Table 2
Mode State Controlling ECM
Position Control Active Engine ECM
Temperature Control Active EFTC
Temperature Control Ambient EFTC
Temperature Control Warm-up EFTC
Temperature Control Regulating EFTC
Temperature Control Cool down 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% for the duration of 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 of 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 CCW direction towards the 0% Position (fully closed). After 46 rotations of the stepper motor the piston will