Operation

Operation

Coolant Flow - Engine Warm Up

During warm-up the coolant pump moves fluid through the cylinder block and it emerges from the inlet manifold outlet pipe. From the outlet pipe, the warm coolant flow is prevented from flowing through the radiator because the thermostat is closed. The coolant is directed into the heater circuit.

Some coolant from the by-pass pipe can pass through small sensing holes in the flow valve, The warm coolant enters a tube in the thermostat housing and surrounds 90% of the thermostat sensitive area. Cold coolant returning from the radiator bottom hose conducts through 10% of the thermostat sensitive area. In cold ambient temperatures the engine temperature can be raised by up to 10°C (50°F) to compensate for the heat loss of the 10% exposure to the cold coolant returning from the radiator bottom hose.

At engine idle speed, the by-pass valve is closed only allowing the small flow through the sensing holes. As the engine speed increases above idle, the greater flow and pressure from the pump overcomes the light spring and opens the by-pass flow valve. The flow valve opens to meet the engines cooling needs at higher engine speeds and prevents excess pressure in the system. With the thermostat closed, maximum flow is directed through the heater circuit.

The heater matrix acts as a heat exchanger reducing coolant temperature as it passes through the matrix. Coolant emerges from the matrix and flows into the coolant pump feed pipe and recirculated around the heater circuit. In this condition the cooling system is operating at maximum heater performance,

Coolant Flow - Engine Hot

As the coolant temperature increases the thermostat opens. This allows some coolant from the outlet housing to flow through the top hose and into the radiator to be cooled. The hot coolant flows from the left tank in the radiator, along the tubes to the right tank. The air flowing through the fins between the tubes cools the coolant as it passes through the radiator.

A controlled flow of the lower temperature coolant is drawn by the pump and blended with hot coolant from the bypass and the heater return pipes in the pump feed pipe. The pump then passes this coolant into the cylinder block to cool the cylinders.

Viscous Fan Operation





When the engine is off the fan is not rotating, the silicone fluid stabilizes within the fluid chamber and the reservoir. The fluid level equalize due to the return port in the valve plate being open between the fluid chamber and the reservoir. In this condition, when the engine is started, silicone fluid is present in the fluid chamber and causes drag to occur between the drive drive plate an the body. This causes the fan to operate initially when the engine is started.

As the fan speed increases, centrifugal force and a scoop formed on the fluid chamber side of the valve plate, pushes the silicone fluid through the return port in the valve into the reservoir. As the fluid chamber empties, the drag between the drive plate and body is reduced, causing the drive plate to slip. This reduces the rotational speed of the fan and allows it to 'freewheel'.

When the coolant temperature is low, the heat emitted from the radiator does not effect the bi-metallic coil. The valve remains closed, preventing fluid escaping from the reservoir into the fluid chamber. In this condition the fan will 'freewheel' at low speed.

As the coolant temperature increases, the heat emitted from the radiator causes the bi-metallic coil to tighten. This movement of the coil moves the valve to which it is attached. The rotation of the valve exposes ports in the valve plate which allow silicone fluid to spill into the fluid chamber. As the fluid flows into the clearance between the annular grooves in the drive plate and body, drag is created between the two components. The drag is due to the viscosity and shear qualities of the silicone fluid and cause the drive plate to rotate the body and fan blades.

As the coolant temperature decreases, the bi-metallic coil expands, rotating the valve and closing off the ports in the valve plate. When the valve is closed, centrifugal force pushes silicone fluid through the return port, emptying the fluid chamber. As the fluid chamber empties, the drag between the drive plate and the body is reduced and the body slips on the drive plate, slowing the rotational speed of the fan.