Contents: When the engine is cold - small… ↳ When the engine is warm - large… ↳ The cooling system is under pressure ↳ The engine temperature is constantly… ↳
The coolant level is clearly visible in the transparent expansion tank next to the right shock absorber dome. If you frequently add small amounts of coolant, check the system for leaks and add antifreeze no later than autumn.
Under normal operating conditions, the Focus' cooling system is always in a healthy temperature range. Cooling is a system consisting of a number of units: the radiator, water pump, radiator fan, thermostat, expansion tank, coolant pipes and hoses are the elements of the plan - the coolant carries out its direct work in the engine block and cylinder head in a filigree network of water channels with precise proportions, in the so-called water jacket. Excess combustion heat, initially accumulated in the water jacket, is then released through the radiator into the atmosphere. The way the coolant circulates depends greatly on the engine temperature.
Schematic representation of the engine cooling system: 1 - heat exchanger - heating; 2 - engine, 3 - thermostat; 4 - water pump; 5 - radiator fan; 6 - expansion tank with coolant.
When the engine is cold - small coolant circulation circuit
After each cold engine start, the coolant first circulates through a small circuit, which is limited by the water jacket and the heating. At this stage, the thermostat closes the path to the radiator until the engine reaches operating temperature.
There is a good reason for this, as there is less coolant in the small circuit - the engine reaches the required temperature faster and emits less exhaust gases. Only when the coolant reaches its operating temperature, the thermostat opens and doses the hot coolant from top to bottom through the radiator. On the way through the heat exchanger, the oncoming wind passing by the radiator fins blows on the hot coolant and takes away excess engine heat from it.
The thermostatically coordinated interaction of water and air protects the engine equally from both cold shock and thermal shock.
When the engine is warm - large coolant circuit
At normal operating temperature, coolant is pumped into the Focus from the coolant box on the right as you drive. From there, it flows into the engine block and into the cylinder head: the vast majority of the fluid returns via the open thermostat to the left coolant box, while the rest passes through the heater heat exchanger. The fluid that flows down in the radiator makes room for the hot fluid at the top. As it passes through the radiator fins, it cools down again, closing the circuit. If the coolant temperature drops below the specified operating temperature during the journey, the thermostat closes until the coolant is warm again.
The cooling system is under pressure
The cooling system is under a certain increased pressure when the engine is running. Due to this, the boiling point of the coolant increases from 100°C to approximately 120°C. The increased temperature allows for a more economical engine operation and, consequently, reduced fuel consumption. If, when the engine is hot, the coolant pressure - depending on the engine version - exceeds 0.85-1.2 bar, the high-pressure valve in the expansion tank cap opens and releases excess system pressure into the atmosphere. The vacuum that occurs when the coolant cools down is equalized by a second, so-called vacuum valve in the cap - it lets atmospheric air into the tank. Often, the oncoming air flow is not enough, especially when driving around town or in traffic jams, to protect the engine from damage due to overheating. For this case, all Focus models have a radiator fan (Zetec-E, double fan) with an electric drive directly behind the radiator. This small wind turbine is activated by a thermal switch at approximately 120°C. The fan switches off again automatically when the normal operating temperature is reached.
Under pressure: the cooling system is checked with a mechanical pump 1. To do this, a pressure of about 1.6 bar is created in the radiator or expansion tank for about 5 minutes. The pressure in the system should drop by about 0.2 bar, otherwise find and eliminate the leak; 2 - expansion tank locking cap.
The engine temperature is constantly monitored
In case the engine temperature is constantly too high under extreme load, for example when towing a trailer, or due to some malfunction, the Focus has an overheating program to protect against major engine damage, stored in the memory of the transmission control unit (PCM). At stage 1, the program sets the temperature indicator needle in the red range of the indicator instrument. If this signal is ignored and the temperature continues to rise, the "Transmission" warning light on the instrument panel lights up. In this case, you must switch off the engine, let it cool down and then go to a Ford workshop. During this time, the control unit did not remain idle, it recorded a fault code in its memory, which Ford workshops read with the FDS2000 diagnostic tool.
But if you consistently ignore or simply do not notice the warning light and the temperature indicator, stage 2 of the program comes into play: the PCM shuts down two cylinders and limits the engine speed to 3000 rpm. At the same time, the warning light - the engine management system (MIL) - comes on - it warns in good time about possible engine damage. In order to cool the engine more effectively, the deactivated cylinders suck in clean air at this time. The cylinders are "paralyzed" in turn in order to achieve uniform cooling of all cylinders. If all this does not impress you, stage 3 comes into play: the "Transmission" warning light starts flashing to show you that you have exactly 30 seconds to pull the Focus to the side of the road, since the engine is completely deactivated to prevent its further damage or seizure.
The original article is available on the website (fordbook.ru)