car thermostat - CarpartsVIP

When the engine is working, the temperature of the cylinder combustion chamber can reach 2000-2500 degrees. Long-term operation will cause the engine temperature to be too high and affect performance, and even damage the parts. The cooling system is responsible for dissipating the heat of each part in time to prevent them from overheating. Common cooling systems are mainly divided into two categories: air cooling system and water cooling system. Because the water cooling system cools evenly, takes effect quickly and has low noise, it is widely used in household engines.

The water cooling system is mainly composed of a water pump, a radiator, a cooling fan, a thermostat, an engine body water jacket, a cylinder head water jacket, and a water pipe loop. After the engine is started, the water pump will be driven to work. Under the action of the water pump pressure, the coolant begins to enter the engine body water jacket from the water pipe. Since the engine body water jacket is distributed around the cylinder, the coolant will absorb heat when it flows through, and then continue to flow into the cylinder head water jacket, and then absorb heat from the cylinder head water jacket again and flow out, and then enter the thermostat. The thermostat is a temperature control valve that can automatically adjust the opening and closing of the valve according to the temperature to control the flow direction of the coolant. When the engine is just started, the temperature of the coolant is low. Under the control of the thermostat, the coolant flows directly back to the water pump, and then flows to the engine body again after being pressurized by the water pump. In this cycle, since the coolant flows in this small range of the water pipe loop, it is called a small cycle. The radiator does not participate in the work during the small cycle, so the heat of the engine will not be lost, which is conducive to engine warm-up. Therefore, in winter, you need to wait a few minutes after starting the vehicle before starting it again. This is conducive to the preheating of various engine parts and has the function of protecting the parts. After the engine has been running for a period of time, the temperature of various parts rises, and the temperature of the coolant also rises accordingly. When a certain temperature is reached, the thermostat will gradually open the valve leading to the radiator. At the beginning, the valve opening is small, and only part of the coolant will flow to the radiator. After the radiator dissipates heat and cools down, it returns to the water pump through the water pipe. This process is called a large cycle.

At the same time, another part of the coolant will flow directly back to the water pump through the thermostat. Therefore, both the large and small cycles will participate in the work in this process, and they work together. When the engine temperature continues to rise and the coolant temperature exceeds the standard value of the thermostat temperature, the thermostat valve will be fully opened, and the valve leading to the water pump will be automatically closed. At this time, all the coolant will flow to the radiator and enter the full large circulation mode. In this process, the coolant passes through the radiator and dissipates heat and cools down under the action of the cooling fan, and the heat is finally dissipated into the air. The cooled coolant continues to flow to the water pump through the pipeline, and the engine’s heat dissipation work continues in this way over and over again. This is the complete working process of the engine cooling system.

In conclusion, the component that prevents the engine from overheating is the thermostat. When it detects that the temperature rises, it will open the valve to start the heat dissipation function, so that the coolant can continue to cool the engine. The small circulation mode of the coolant is conducive to the preheating of the engine. It is best to warm up the engine for a few minutes before driving in winter, which helps protect the parts. The large circulation mode of the coolant system is a complete heat dissipation mode, at which time the cooling system fully dissipates heat for the engine.

In the engine cooling system, the element that controls the flow of coolant is called a thermostat. The thermostat is a temperature-controlled valve that can automatically adjust the opening and closing of the valve according to the engine load and the temperature of the coolant to control the flow of the coolant to achieve large and small cycles. In layman’s terms, the thermostat is a three-way valve, one side of which is connected to the engine water outlet, one side is connected to the water inlet of the water pump, and one side is connected to the radiator. It can adjust the direction of the water flow according to the water temperature. When the water temperature is low, the coolant flows downward to achieve a small cycle; when the water temperature is high, the coolant flows upward to achieve a large cycle. It is usually installed in the engine water circuit to control the engine temperature. The engine mainly uses paraffin thermostats, which use the thermal expansion and contraction characteristics of paraffin to open and close the valve. Paraffin thermostats are divided into two categories: mechanical and electronic. Their implementation principles are the same, but the difference lies in the different trigger mechanisms of paraffin heating. First, let’s look at the mechanical thermostat. Let’s look at its components. It is a container, and the substance inside is paraffin. At low temperatures, paraffin becomes solid. Under the action of the spring, the thermostat valve closes the coolant channel between the engine and the radiator. The coolant returns to the engine through the water pump for a small cycle in the engine. At high temperatures, the paraffin melts and expands and gradually becomes liquid. The volume increases and compresses the rubber tube to shrink. While the rubber tube shrinks, it pushes the push rod upward. The push rod pushes the valve downward to open the valve. At this time, the coolant passes through the radiator to the thermostat valve and then circulates through the water pump to the engine for a large cycle. The main valve, return spring, base, lower bracket, bypass valve spring, bypass valve and other components form a whole and are sealed in the thermostat air shell. The base and lower bracket are fixed and play a fixing role. They cannot move during operation.

The linkage effect of the mechanical thermostat: The thermostat is held upward by the return spring and fixed to the base by the push rod passing through the piston. At low temperatures, the main valve and the base are sealed, and the bypass valve below and the wall of the sewer pipe are open. At this time, the coolant enters and exits to form a small cycle. When the temperature rises, the paraffin begins to melt and expand, and the piston will be pushed upward under the action of the expansion tension. Since the piston is fixed by the push rod and cannot move, the thermostat will be forced to move downward under the action of the reverse thrust. The thermostat moves downward under the action of the reverse thrust. At this time, the main valve is separated from the base, resulting in a certain opening, and the bypass valve below is combined with the wall of the sewer pipe to produce a certain degree of closeness. Since the water temperature at this time has not reached the peak value of the thermostat, the main valve above and the bypass valve below are not fully opened and closed, so the coolant will flow in two directions. At this time, the large and small cycles work at the same time. When the water temperature continues to rise and exceeds the thermostat peak, the main valve will be fully opened and the bypass valve below will be fully closed. At this time, all the coolant will flow through the main valve to the radiator and enter a full circulation mode. The above is the implementation principle of the mechanical paraffin thermostat.

Tag Archives: car thermostat

How does the common water cooling system work? What are the big cycle and the small cycle?

How does the thermostat control the flow of coolant?