90131-896-650 Honda SEE PART DETAILS - PRI; BOLT, DRAIN PLUG (Honda Code 1986231).

Illustration 1 g01932599
Cooling system for a warm engine
(1) Cylinder head
(2) NRS Cooler
(3) Water temperature regulator housing
(4) Expansion tank
(5) Shunt line
(6) Bypass
(7) Radiator
(8) Cylinder block
(9) Oil cooler
(10) Water pump During operation, water pump (10) sends most of the coolant from radiator (7) to oil cooler (9).The coolant from oil cooler (9) goes into cylinder block (8) through a bonnet and an elbow. The coolant flows around the cylinder liners into the cylinder head.The flow of coolant into the head goes around the valves and the passages for exhaust gases in the cylinder head. The coolant then goes to the front of the cylinder head. At this point, the water temperature regulators (3) control the flow of the coolant into the radiator (7).The coolant flows from the cylinder block into the NRS cooler. The coolant flows from the NRS cooler back to the cylinder block.Water temperature regulators (3) are closed when the engine is cold. The coolant flows through the regulator housing and the elbow back to water pump (10). This is done in order to increase the operating temperature of the engine coolant.If the coolant is at normal operating temperature, water temperature regulators (3) open and the coolant flows to radiator (7) through the outlet hose. The coolant becomes cooler as the coolant moves through the radiator. When the coolant gets to the bottom of the radiator, the coolant goes through inlet hose and into water pump (10).Note: Water temperature regulators (3) are an important part of the cooling system. Water temperature regulator (3) divides the coolant flow between radiator (7) and bypass elbow (6). This will maintain the correct temperature.Shunt line (5) gives several advantages to the cooling system. The shunt line gives a positive coolant pressure at the water pump inlet that prevents pump cavitation. A small flow of coolant constantly goes through shunt line (5) to the inlet of water pump (10). This causes a small amount of coolant to move constantly through the vent tube. The flow through the vent tube is small and the volume of the upper compartment is large. Air in the coolant is removed as the coolant goes into the upper compartment.The vent line is used to fill the cooling system with coolant for the first time. This will purge any air out of the top of a bottom filled system.The OEM may supply a surge tank. The tank can be mounted on the radiator or the tank can be mounted on a remote location. The coolant that expands past the radiator cap is retained in the surge tank. The coolant contracts as the temperature drops and the coolant is drawn back into the radiator.Coolant For Air Compressor
Illustration 2 g01321248
Coolant flow in air compressor
(14) Air compressor
(15) Outlet hose
(16) Inlet hose The coolant for air compressor (14) comes from the cylinder block through inlet hose (16) and into the air compressor. The coolant goes from the air compressor through outlet hose (15) back into the front of the cylinder head.Coolant for the Turbocharger
Coolant for the turbocharger comes from a connection that is after the water pump. This connection is before the engine oil cooler. The coolant flows through a hose to the turbocharger cartridge. The cartridge has two inlets and two outlets. An inlet and an outlet are used for coolant flow. The coolant cools the turbocharger cartridge. The other inlet and the other outlet are used for lubrication of the bearings.