What is a thermostat and what is it for?


The thermostat is one of the elements of the engine cooling system. This device allows you to maintain the operating temperature of the motor while it is running.

Consider what function the thermostat performs, its structure, and possible malfunctions.

What it is?

In short, a thermostat is a valve that reacts to changes in the temperature of the environment in which it is located. In the case of a motor cooling system, this device is installed at the junction of two pipe hoses. One forms the so-called small circle of circulation, and the other - a large one.

What is a thermostat and what is it for?

What is a thermostat for?

Everyone knows that the engine gets very hot during operation. So that it does not fail from an excessively high temperature, it has a cooling jacket, which is connected with pipes to the radiator.

As a result of vehicle standstill, all lubricant gradually flows into the oil pan. It turns out that there is practically no lubricant in a cold engine. Considering this factor, when the internal combustion engine starts up, it should not be given heavy loads so that its parts do not wear out faster than usual.

The cold oil in the sump is more viscous than when the power unit is operating, so it is more difficult for the pump to pump it into all units. To speed up the process, the engine must reach operating temperature as quickly as possible. Then the oil will become more fluid and the parts will lubricate faster.

The first car designers faced a difficult task: what to do to make the engine warm up quickly, but its temperature was stable during operation? For this, the cooling system was modernized, and two circulation circuits appeared in it. One provides fast heating of all sections of the engine (antifreeze or antifreeze is heated from the hot walls of the cylinders and transfers heat to the entire body of the internal combustion engine). The second is used to cool the unit when it reaches operating temperature.

What is a thermostat and what is it for?

The thermostat in this system plays the role of a valve, which at the right time deactivates the heating of the engine and connects the radiator to maintain the operating temperature of the internal combustion engine. How is this result achieved?

The device and principle of operation of the thermostat

The thermostat design includes:

  • Cylinder Basically, its body is made of copper. This metal has good thermal conductivity.
  • There is a filler inside it. Depending on the model of the part, it can be made from water and alcohol, or it can be from wax mixed with powder of copper, aluminum and graphite. This material has a high coefficient of thermal expansion. As long as the wax is cold, it is hard. It expands as it heats up.
  • Metal stem. It is placed inside the cylinder.
  • Rubber compressor. This element prevents the filler from entering the coolant and moves the stem.
  • Valve. There are two of these elements in the device - one at the top of the thermostat, and the other at the bottom (in some models it is one). They open / close the small and large circuit.
  • Housing. Both valves and the cylinder are fixed on it.
  • The springs provide the necessary resistance to stem movement.
What is a thermostat and what is it for?

The whole structure is placed inside the junction between the small and large circle. On the one hand, a small loop inlet is connected to the unit, on the other, a large inlet. There is only one way out of the fork.

While the coolant circulates in a small circle, it gradually heats up the thermostat cylinder. Gradually the temperature of the environment rises. When the indicator reaches 75 to 95 degrees, the wax has already melted (metal granules accelerate the process) and begins to expand. Since it lacks space in the cavity, it presses against the rubber stem seal.

When the power unit has warmed up sufficiently, the large circle valve begins to open, and the antifreeze (or antifreeze) begins to move in a large circle through the radiator. Since the operation of the stem directly depends on the temperature of the liquid in the channel, the device allows you to maintain the optimum temperature of the motor at any time of the year: in summer it does not allow it to overheat, and in winter it quickly reaches the operating temperature.

Regardless of the thermostat modifications, they all work according to the same principle. The only difference between them is the temperature range at which the valve is triggered. This parameter depends on the brand of the engine (each of them has its own operating temperature, therefore, the valve must also open within the specified range).

Depending on the region in which the car is operated, the thermostat should also be selected. If the main part of the year is hot enough, then a thermostat should be installed that works at a lower temperature. In colder latitudes, on the contrary, so that the engine warms up sufficiently.

What is a thermostat and what is it for?

To prevent the motorist from installing an unsuitable part, the manufacturer indicates the valve opening parameter on the device body.

In addition, all thermostats are different from each other:

  • The number of valves. The simplest design is with one valve. Such modifications are used in old cars. Most modern cars use a two-valve version. In such modifications, the valves are fixed on one stem, which ensures their synchronous movement.
  • One and two steps. Single stage models are used in classic cooling systems. If the fluid flows under pressure in the circuit, then two-stage thermostats are installed. In such models, the valve consists of two elements. One of them is triggered with less effort to relieve pressure, and then the second is activated.
  • With and without a body. Most of the models are frameless. To replace it, you need to disassemble the assembly in which it is installed. To facilitate the task, manufacturers implement some modifications already assembled in a special block. It is enough to connect the corresponding connections.What is a thermostat and what is it for?
  • Heated. Some vehicles are fitted with thermostats with a temperature sensor and a cylinder heating system. Such devices are controlled by an ECU. The main task of such devices is to change the temperature range of valve opening. If the motor is running without heavy loads, the thermostat is operating normally. If there is an additional load on the unit, the electronic heating forces the valve to open earlier (the coolant temperature is approximately 10 degrees lower). This modification saves a little fuel.
  • Sizes. Each cooling system uses pipes of not only different lengths, but also diameters. In connection with this parameter, a thermostat must also be selected, otherwise antifreeze will flow freely from a small circuit to a large one and vice versa. If a body modification is purchased, then the diameter of the pipes and their angle of inclination will be indicated in it.
  • Complete set. This parameter is vendor dependent. Some sellers sell devices with high quality gaskets, while others put a lower-quality consumable in the kit, but offer to buy a more durable analog.

Checking the thermostat in the car

There are two ways to check the health of a device:

  • By dismantling from the system;
  • Without removing from the car.

The first method is rarely used. Some resort to it to fully make sure that it works. Also, this method will allow you to check the performance of a new part, since this will not work in the store. To do this, you need to heat the water (boiling water - above 90 degrees). The part is dipped into a container of boiling water.

If after a couple of minutes the valve does not open, then the part is faulty - either something happened to the stem, or to the spring, or maybe something happened to the container in which the wax is located. in this case, the thermostat must be replaced with a new one.

For more details on how to check a new part, see the video:

Checking the car thermostat

How to determine if it works or not?

You don't need to be a leading mechanical expert to test the thermostat on the machine without removing it. It is enough to understand how the device works. During the first minutes of engine operation, the entire cooling system should not heat up. With this in mind, you need to do the following:

  1. Start the engine and let it run.
  2. At this point, you should try the pipes connected to the radiator. If the thermostat is good, the system will not heat up for up to five minutes (depending on the ambient temperature). A cold system indicates that the valve is closed.
  3. Next, we look at the arrow on the dashboard. If it rises quickly and goes far beyond the 90 degree mark, try the pipes again. A cold system indicates that the valve is not responding.What is a thermostat and what is it for?
  4. Ideally, the following should happen: while the engine is warming up, the cooling system is cold. As soon as it has reached the desired temperature, the valve opens and antifreeze goes along a large circuit. This cools the bypass gradually.

If there are irregularities in the order of the thermostat, it is better to replace it immediately.

What are the types of malfunctions?

The thermostat is an unpretentious part in a car. Its working resource can be quite large. Nevertheless, due to various circumstances, it can fail. Here are some reasons for the breakdown:

  • Scale. Most often, this problem occurs due to the negligence of the motorist. Poor-quality antifreeze (or even water at all) and violation of the fluid change regulations lead to the formation of various deposits on the stock. Because of this, the valve may not open on time or not react at all to temperature changes.What is a thermostat and what is it for?
  • Vibration. This effect cannot be eliminated during engine operation, therefore this factor will only affect the defective part.
  • Overheating of the coolant. In the case of an old thermostat, breakage is inevitable, since the rubber seal is destroyed due to high temperatures. This also applies to the seal that drives the stem.

If the thermostat is broken, it can be either open or closed. In the first case, the motor will take too long to warm up (antifreeze moves immediately through the radiator and cools down).

In the second case, the motor will constantly overheat (the temperature arrow will jump up almost after a few minutes, and subsequently will show the maximum). In this case, the radiator and expansion tank will be cold.

What is a thermostat and what is it for?

There is also another symptom of a faulty thermostat. At idle, the engine takes a long time to warm up, but as soon as it experiences an increased load, the cooling stops working, and the arrow jumps up sharply. In this case, the thermostat is stuck in the middle position. It does not warm up quickly, because the coolant goes in a large circle. But the half-open valve is not enough for good cooling.

An indirect sign of a thermostat malfunction may be incorrect heating operation - cold air comes out of the air ducts, although the motor has been running for a long time.

Whatever the malfunction, it cannot be tolerated, since driving on a cold engine increases the wear of its parts, and working at extreme temperatures threatens to quickly break down the engine.

Video - checking work

A breakdown of the thermostat is critical for the engine. In addition, read a detailed overview of how the thermostat works as well as the test options:

Thermostat. Device, principle of operation, malfunction, check


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