Patent ID: 6843209

Claim:
An engine cooling water passage structure for connecting to a water jacket and a radiator comprising: a cooling water passage unit including; a cooling water supply passage; a water pump for connection to the cooling water supply passage; a thermostat housing in the cooling water supply passage for housing a thermostat wherein the cooling water passes through the water pump and through the thermostat housing when being supplied from the radiator to the water jacket; a cooling water discharge passage for discharging cooling water from the water jacket into the radiator; and a bypass passage operably couple between the water jacket and the thermostat housing, for returning the cooling water from the water jacket to the thermostat housing and bypassing the radiator; wherein the cooling water passage unit is formed of a plurality of divided sections, said divided sections being previously and integrally formed as a sub-assembly and this sub-assembly being detachably mounted as a unit on an engine main body, wherein the cooling water passage unit comprises a mating surface that is joined to the engine main body, and the cooling water supply passage and the cooling water discharge passage of the cooling water passage unit communicate with the water jacket of the engine main body via the mating surface.