General
The VRSCA engine is cooled by a an ethylene-glycol coolant and the lubricating engine oil.
The ethylene-glycol coolant is pressurized and circulated through the engine and a cooling radiator by an impeller type water pump utilizing a thermostat controlled bypass.
The coolant pressure determines the coolant boiling point. The boiling point rises as the pressure increases and drops as the pressure decreases. At the rated system pressure of 103 kPa (15 psi), the boiling point rises to over 121°C (250°F).
The engine oil also cools the engine. Specifically, an oil jet under each piston sprays a mist of oil to lower the operating temperature of that piston. See 3.4 Oil flow.
Flow description
![](https://motoinstruction.ru/img/harley/2/111179.jpg)
Figure 6-1. Engine coolant flow: 1. Red - hot coolant; 2. Blue - cooled coolant; 3. Water pump; 4. Thermostat; 5. Coolant inlet pipe; 6. Pressure cap; 7. Overflow tube; 8. Overflow bottle; 9. Overflow bottle vent tube; 10. Coolant outlet pipe; 11. Radiator; 12. Combustion chamber coolant passages; 13. Cylinder coolant passages
See Figure 6-1. To warm the engine up quickly, the ethyleneglycol coolant is re-circulated through the cylinders (13) and combustion chamber (12) in the cylinder heads. The thermostat (4) blocks the passage to the radiator (11) to recirculate the coolant.
As coolant exits the pump (3), it flows through the crankcase and around the cylinder liners (13) removing the heat build-up caused by the motion of the piston rings. From the cylinder liners (13), the coolant flows up through the cylinder head and around the exhaust valves and combustion chamber (12). After the coolant passes around the combustion chamber (12), it then flows back through the closed thermostat (4) into the pump (3) to repeat the cycle. This flow continues until the coolant reaches 85°C (185°F) and the thermostat (4) opens.
Once the coolant exceeds 100°C (212°F), the thermostat (4) remains open and blocks the by-pass between the entrance and exit ports of the case.
An engine coolant temperature (EOT) sensor is mounted to the thermostat (4). If the temperature should exceed 112.7°C (235°F), the engine coolant temperature indicator on the instrument cluster will illuminate.
After the coolant leaves the cylinder heads, it flows through the radiator coolant inlet pipe (5) to the radiator (11).The ethylene-glycol is cooled as it flows through the radiator (11) from left to right.
To increase the amount of air flowing through the radiator (11), two cooling fans will turn on when the coolant temperature exceeds 96°C (205°F) and will turn off when the temperature drops below 91°C (195°F).
The coolant exits the top right of the radiator (11) and flows through the radiator outlet coolant pipe (10) to the coolant pump (3) inlet.
The pressure cap (6) and radiator filler neck pressurize the coolant system. When the coolant pressure exceeds the pressure cap (6) lower limit of 96 kPa (14 psi), the lower valve opens and the excess pressure and expanded coolant flow to the overflow bottle (8) through the overflow tube (7). The overflow bottle (8) is vented to the atmosphere through a long tube (9) which loops over the top of the radiator/oil cooler assembly and down below the coolant level. When the pressure drops, the pressure cap (6) vacuum valve opens to draw coolant back into the coolant inlet pipe (5) from the overflow bottle (8).