Device Features
Pressurized closed cooling system. There is a safety valve in the plug of the expansion tank. The engine cooling system includes a passenger compartment heating radiator, which is located under the instrument panel.
Filling volume of the engine cooling system:
- K4M and K7M (complete with air conditioning) - 5.45 l;
- K4M and K7M (equipment without air conditioning) - 4.5 l.
The temperature at which the thermostat valve starts to open is 89°C.
Full opening temperature of the thermostat valve - 99±2°C.
The calibration value of the valve in the plug of the expansion tank is 1.4 bar.
Engine 1.6 (16V)
Engine 1.6 (8v)
Figure 13-1 - Scheme of the engine cooling system: 1 - engine; 2 - water pump; 3 - thermostat; 4 - fitting for removing air; 5 - heater radiator; 6 - radiator of the engine cooling system; 7 - expansion tank
Purpose and principle of operation of the cooling system
The efficiency of the cooling system depends on its design and operating conditions. The design of the cooling system is determined by the engine power, the size of the cooling radiator, the type of coolant used and the power of the water pump (coolant circulation pump), fan type, thermostat and system pressure. Unfortunately, the cooling system is usually overlooked until problems arise. Proper routine maintenance can prevent these problems from occurring.
The cooling system must allow the engine to warm up to the required operating temperature as quickly as possible and then maintain that temperature. It must operate effectively in an ambient temperature range of -30°F (-35°С) up to 110°F (45°С).
The maximum combustion temperature in the engine intermittently soars to levels ranging from 4000°F to 6000°F (from 2200°С to 3000°С). The average combustion chamber temperature ranges from 1200°F to 1700°F (from 650°С to 925°С). Prolonged heating to such high temperatures would cause a decrease in the strength of engine parts, so it is necessary to remove heat from the engine. The cooling system maintains the temperature of the walls of the combustion chamber in a temperature range that ensures maximum engine efficiency (pic. 7.1).
Pic. 7.1. Typical mixture combustion temperature and typical exhaust gas temperature at the exhaust port
Engine Problems at Low Operating Temperatures
For the engine to operate normally, its operating temperature must be above a certain minimum allowable level. If the operating temperature is too low, then there is not enough heat for the normal evaporation of the fuel required to obtain the desired composition of the fuel-air mixture. As a result, it is necessary to increase the fuel consumption in order to create a concentration of its vapors that ensures the flammability of the working mixture. The heavier, less volatile components of gasoline do not evaporate and remain as unburned liquid fuels. In addition to this, part of the working mixture, in contact with the cold walls of the engine, cools down, which leads to incomplete combustion of the fuel and the formation of soot.
The combustion of gasoline is a violent oxidative process, which is a chemical reaction of the combination of hydrocarbon fuels with oxygen contained in the air. This reaction takes place with the release of heat. When burning five liters of fuel, one liter of water is produced in the form of vapours. Some of this moisture condenses and enters the oil pan along with unburned fuel and soot, resulting in sludge deposits. Condensed moisture reacts with unburned hydrocarbons and additives, resulting in the formation of acids: carbonic, sulfuric, nitric, hydrobromic and hydrochloric. These acids are responsible for engine wear caused by internal corrosion and rusting. When the coolant temperature drops below 130°F (55°С), rust appears immediately. Below 110°F (45°С) water formed during the combustion of fuel accumulates in the oil. When the coolant temperature is below 165°F (65°С) rapid wear of the cylinder walls.
To mitigate the negative processes in the engine associated with low temperatures and to facilitate starting the engine in cold weather, most manufacturers offer cylinder block heaters as additional engine equipment. These heaters are connected to a conventional electrical network (110 V AC mains) and the heating element heats up the coolant (pic. 7.2).
Pic. 7.2. In order to remove the heating element, it is necessary to unscrew the screw with which it is fastened in the technological hole in the wall of the cylinder block (A). The heating element is removed from the cylinder block. The coolant, heated by the heating element immersed in it, expands and, rising up, displaces the cold coolant. Due to convective heat transfer, the coolant is heated throughout the engine (b)
Engine Problems at High Operating Temperatures
To protect the motor from overheating, its operating temperature must not exceed the maximum allowable temperature. High temperatures cause oil to oxidize. Under their action, the dissociation of the oil occurs with the formation of coke and drying oil. With prolonged overheating, coke is deposited on the piston rings, clogging them. Lacquer deposits cause hydraulic valve lifter plungers to seize. High-temperature heating inevitably leads to a decrease in the viscosity of the oil and a decrease in the thickness of the lubricant layer. If the lubricant layer becomes too thin, dry contact between the surfaces of the moving parts occurs. At the same time, the coefficient of friction increases, which causes a decrease in engine power and accelerated wear of its components.
Engine overheating is costly
Failure of the cooling system is the main cause of engine failure. Auto mechanics are often tormented by nightmares - they dream about how, in a service center, an engine they have just repaired is put into a car whose radiator is clogged. After a bulkhead or repair of the engine, as a rule, a mandatory replacement of the water pump and all hoses is made. Any engine repair or replacement should also check the radiator for leaks and blockages. Overheating is the most common cause of engine failure.
Cooling system design
The coolant flows through the engine, absorbing the heat generated in it. It then flows into a heatsink, which dissipates the heat to the environment. Coolant circulates continuously through the cooling system as shown in fig. 7.3 and 7.4. As the coolant passes through the engine, it heats up by as much as 15°F (8°C). Passing then through the radiator, it cools down. Coolant pumping speed can reach 4 liters per minute per one horsepower of power generated by the engine.
Pic. 7.3. Scheme of the flow of coolant through the engine
Pic. 7.4. The photo of this cylinder block, from which the plate has been cut, shows the cooling system channels surrounding the cylinders. Pay attention to the fact that the coolant washes the cylinders from all sides and passes also in the gaps between them
Engine temperature and exhaust toxicity
In many areas there is a control of the toxicity of vehicle exhaust gases. Emissions of hydrocarbons (NS) It's just unburned fuel. To reduce unburnt hydrocarbon emissions and pass emissions tests, ensure that the engine is warmed up to normal operating temperature before passing the tests. Car manufacturers define achievement "normal operating temperature" on the following grounds:
- 1. Upper radiator hose gets hot and pressurized.
- 2. Electric fan turns on and off twice (fans) cooling systems.
Ensure that the engine has warmed up to normal operating temperature before undergoing an emission test. Best to drive 20 miles (32 km), - then the catalytic converter, oil, and coolant will certainly warm up to normal operating temperature. It is especially important to take care of this in cold weather. Most drivers find that to warm up the engine, it is enough to let it idle until warm air comes out of the passenger compartment heater. The interior heater extracts heat from the coolant. Car manufacturers recommend not allowing the engine to idle for more than 5 minutes, and to warm up the engine, let it idle for one to two minutes, after which, for further warming, it is necessary to drive the car slowly to increase the oil pressure in the lubrication system.
Hot coolant flows through the thermostat valve at the highest point of the engine into the radiator. The outlet pipe of the cooling system is connected to the upper inlet pipe of the radiator by a hose, which is fixed with clamps. The coolant is cooled in the radiator by the flow of air blowing it. As it cools, it sinks down the radiator and through the lower outlet pipe enters the water pump, which provides forced circulation of the coolant in the engine.
Note
Some newer engine designs have a thermostat installed at the water pump inlet. When the coolant enters the thermostat, it closes and remains closed until the temperature of the coolant reaches its opening temperature. Thus, placing a thermostat at the water pump inlet reduces the range of temperature fluctuations in the coolant, attenuating sudden changes in temperature that could cause thermal stresses in the engine, especially in engines with an aluminum cylinder head and a cast iron block.
The efficiency of heat removal by the cooling system is determined mainly by the efficiency of the radiator. Radiator designs are designed to provide maximum heat transfer efficiency with minimum dimensions. Radiator airflow is enhanced by a belt-driven or electric-driven cooling fan.