Fig. 5.21. Engine cooling system: 1 – radiator outlet hose; 2 – liquid hose of the expansion tank; 3 – thermostat; 4 – water pump; 5 – expansion tank; 6 – water jacket outlet pipe; 7 – radiator supply hose; 8 – shut-off valve; 9 – electric fan; 10 – expansion tank steam hose; 11 – radiator
The engine cooling system is liquid, closed type, with forced circulation of liquid. The design of the cooling system is shown in Fig. 5.21. The system consists of a cooling jacket, radiator 11 with electric fan 9, expansion tank 5, water pump 4, thermostat 3, outlet pipe 6 of the water jacket, shut-off valve 8 and hoses.
The circulation of liquid in the system is created by water pump 4. From the pump, liquid is fed into the engine cooling jacket, washes the cylinders of the combustion chamber and then goes to thermostat 3. Depending on the position of the thermostat valve, liquid goes either to the water pump (at low temperature) or to the radiator 11 (at high temperature).
Radiator 11 with horizontal liquid flow, with tubular-ribbon aluminum core and plastic tanks. In the lower part of the left radiator tank there is a drain plug. The tanks contain the supply and outlet hose pipes to the engine water jacket, the steam hose pipe 10 connecting the radiator with the expansion tank.
Expansion tank 5 serves to compensate for the changing volume of the coolant depending on its temperature. It is made of translucent plastic. The inlet and outlet valves are installed in the plastic cap of the tank, which closes its neck.
NOTE: The serviceability of the expansion tank cap valves is very important for the normal operation of the cooling system. However, when problems arise (for example, boiling coolant), car enthusiasts pay attention only to the operation of the thermostat and forget to check the valves. A leaky outlet valve leads to a decrease in the boiling point of the coolant, and its jamming in the closed position leads to an emergency increase in pressure in the system, which can cause damage to the radiator and hoses.
Water pump 4 centrifugal type provides forced circulation of liquid in the cooling system. It is located on the front surface of the cylinder block and is driven by a poly V-belt, common with the generator and the power steering pump, from the crankshaft pulley. The pump has sealed bearings that do not require replenishment of lubricant. The pump is not subject to repair, therefore, in case of failure (fluid leakage or damage to the bearings), it is replaced as an assembly.
Thermostat 3, which is an electromagnetic valve, maintains the normal operating temperature of the coolant and reduces the engine warm-up time. The thermostat is controlled by the electronic unit of the engine control system, which receives information from the coolant temperature sensor installed on the outlet pipe 6 of the water jacket. The thermostat is installed in a housing fixed to the cylinder head. At a coolant temperature of up to 60°C, the thermostat is completely closed and the liquid circulates along a small circuit, bypassing the radiator, which accelerates engine warm-up. At a temperature of about 80°C, the thermostat begins to open, and at 98°C it opens completely, ensuring circulation of liquid through the radiator.
Electric fan 9 cooling system (with a plastic eight-blade impeller) serves for additional blowing of the radiator, is switched on and off by the signal of the electronic engine control unit. Moreover, depending on the intensity of the thermal mode and the algorithm of the air conditioner, the electric fan can rotate at low and high speed. Changing the fan speed mode is ensured by the engine control unit by connecting an additional resistor. The electric fan assembled with the casing is fixed on the radiator of the cooling system.
Outlet pipe 6 water jacket serves to distribute coolant flows depending on the operating modes of the cooling system. A coolant temperature sensor is screwed into the body of the pipe, according to which the electronic unit of the engine control system controls the thermal mode of the engine.
Shut-off valve 8 is designed to stop the coolant draining into the expansion tank when starting a cold engine. The shut-off valve in the closed state reduces the circulation of coolant in the system of an unheated engine, which allows saving fuel when warming up the engine and reduces the warm-up time. At a coolant temperature of 80°C, the shut-off valve opens completely and the liquid begins to circulate through the expansion tank.
The interior heater radiator is also connected to the cooling system via hoses.
The system is filled with a liquid (antifreeze) that does not freeze at ambient temperatures down to -40°C. The type of coolant poured into the cooling system is Motorcraft Super Plus 4 (green) or Motorcraft Super Plus 2000 (orange).
WARNING: Motorcraft Super Plus 4 is a non-silicified organic acid (OAT) based coolant and should not be mixed with other types of coolant.
Motorcraft Super Plus 2000 is a monoethylene glycol based coolant, like most modern coolants.
NOTE: The procedure for replacing the coolant is described in Section 4, Maintenance (see "Replacing the coolant").
WARNING: It is not recommended to fill the cooling system with water, as the antifreeze contains anti-corrosion, anti-foaming and anti-scale additives.
WARNING: Coolant is toxic! Avoid inhalation of vapors and skin contact.
WARNING: Repair any leaks in the cooling system promptly to avoid coolant vapors getting into the car's interior during operation. Your health is more valuable than a new cooling system hose or a tube of sealant!
The electronic engine control unit has a program to protect the engine from overheating. At the very beginning of overheating, based on information from the coolant temperature sensor, the engine control unit sends a command to move the coolant temperature indicator needle to the red zone.
Fig. 1.8. Instrument cluster
If the driver does not stop the engine and its temperature continues to rise, the engine control unit turns on the control lamp 16 (see Fig. 1.8), this indicates to the driver that the engine is approaching a critical limit and must be stopped.
If the driver ignores the coolant temperature gauge and the lamp, the electronic engine control unit cuts off the fuel supply to two engine cylinders and limits the crankshaft speed to 3000 min⁻¹. At the same time, the engine malfunction indicator lamp 24 (see Fig. 1.8) lights up, indicating the possibility of significant engine damage and a sharp increase in exhaust gas toxicity. In this mode, air is sucked into the disabled cylinders, which reduces the engine temperature. Moreover, the disabled cylinders alternate with each other for more uniform cooling.
NOTE: If the engine has gone into two-cylinder mode, it can only be returned to four-cylinder mode by turning the ignition off and on again.
If the engine temperature continues to rise after all measures have been taken, the control unit switches off the engine. If at this time the throttle control pedal has moved to a large angle by pressing the foot (for example, the driver is overtaking), the engine will be stopped only 10 seconds after releasing the pedal.