Gilera 633721 Workshop Manual page 328

Cooling system
Circuit diagram
The cooling system is a forced circulation type system, with continuous venting and air pressurisation.
Circulation takes places by a centrifugal pump driven by the countershaft.
The pump delivers the coolant to the thermal group.
The two-way thermostat support is connected in output to the head. One way is connected to the pump
and the other to the radiator (of the horizontal circulation type).
The radiator output is directly connected to the pump.
The expansion tank is connected in parallel to the radiator.
The radiator hot box is connected to the upper side of the expansion tank (in air).
The radiator cold box is connected to the lower side of the expansion tank (in the fluid).
When the engine is cold, the thermostat output to the radiator is closed, even though there is still a little
flow for de-aeration obtained by a hole into the closing plate.
In this case, the circulation into the thermal group is active to ensure an even heating.
Once the working temperature has been reached, the main circulation on radiator and expansion tank
starts.
With the small openings in the thermostat there is a flow overlapping (recirculation and main one).
When the temperature is higher, the thermostat allows excluding the recirculation to favour the main
circulation.
In this case, the flow is consistent in the expansion tank as well, and this ensures a continuous automatic
venting.
COOL SYS - 328
Nexus 500 euro 3