System Description; System Filling Rule - PIAGGIO 500 cc Service Manual

Cooling

System description

The cooling system is made with a centrifuge pump coaxial to the counter shaft and as such completes a number
of revolutions identical to that of the driving shaft.
The pump has two ducts, one for inlet and one for outlet.
The outlet duct feeds the cylinder and consequently the head; the inlet duct leads from the head and its entrance
to the pump is controlled by the thermostat plate.
The main seal of the thermostat acts instead on the main pump inlet duct leading from the radiator.
The radiator is fed from the head outlet; the expansion tank is inserted parallel to the radiator with the ducts on two
levels: the delivery high up (in the air) and the fluid backflow low down (in the fluid).
The system composed in this way is a 2-way type.
The first way is the internal engine circulation and involves the pump, cylinder and head; this circulation is fully active
when the thermostat is fully closed.
The second way is active with the thermostat fully open and is the main circulation which involves the pump, cylinder,
head, radiator and expansion tank; for medium openings of the thermostat, however, the two circuits are both partially
inserted, therefore the two ways are superimposed.
This kind of circuit is defined as the type with inlet thermostat. The thermostat is crossed by an inverted flow, that
is with cold water which tends to lower the temperature of the wax cell.
This system allows optimization of the engine heating phases.
The expansion tank, parallel to the radiator and inserted on the main circuit, guarantees self-drainage when working.
For the filling stages of the system there are two drains: one on entry to the pump and one exiting from the head (see
filling rules).
The electrical fan is operated by the fuel injection system with temperature measured on the engine head.

System filling rule

- Prepare the 50-50 mixture of water and coolant;
- Fill the system up to the level between MIN and MAX
shown on the filling hole of the expansion tank;
- Do not close the expansion tank with the plug.
- Loosen the drain screw situated on the pump intake
sleeve controlled by the thermostat;
- Keep it open until the air discharge has stopped
completely;
- Retighten the drain screw.
11 - 4
MAX
MIN
05_492
05_493