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How to check the expansion tank cap. The device and principle of operation of the expansion tank


How well do vehicle owners know their car? After all, she is also prone to various diseases, from which it is necessary to get rid of in a timely manner. The cooling system of any car (domestic or foreign production) deserves attention. It includes a special container, which is simply impossible to do without, since it has the main role. However, any element of the system performs its task, and without them it is impossible to effectively cool the engine. And if experienced drivers know how to check the expansion tank cap, then beginners may encounter difficulties.

The ability is simple, but this does not detract from its importance. Many motorists consider the pump and radiator to be the most important components of the cooling system. They are right? And what secrets can hide such an inconspicuous and small detail as the cap of the expansion tank?

A small introduction

The expansion tank (RB) looks pretty simple: cheap and cheerful. But, despite this, it is impossible to simply take it and throw it out of the car. In such insignificant, at first glance, details, there can be problems, and there are a lot of them. Often they simply explode from high pressure, and the coolant (coolant) begins to fill the entire engine compartment.

For this reason, you should not wait until the tank shows itself at the most inopportune moment. If a problem is discovered, there is no need to postpone its solution indefinitely.

But before we figure out how to check the expansion tank cap of the VAZ 2110 (or any other model), let’s find out what it is for and what an important role it plays. Maybe it would be better without him?

An important element of the system

No one will argue that the engine cannot be cooled without cooling, since it is necessary to maintain a certain temperature. A special liquid successfully copes with this. Several decades ago, ordinary water was used for these purposes, and the upper tank of the radiator, which was not completely filled, was used as a compensator. Now drivers prefer antifreeze or antifreeze.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

And here it is worth clarifying something. According to the laws of physics, a liquid expands when heated, and when boiled, it completely turns into steam. If water is heated to a temperature of 100°C, its volume will increase by 4.5%. The same thing happens with the liquids used, only a little more – 6%.

This leads to an increase in pressure in the cooling system. For this reason, additional space is required if the liquid volume is increased. This is what the expansion tank is for. Compensates for the increased volume of antifreeze or antifreeze.

Tank device

To check the expansion tank cap of an Audi or any other car, you need to know how it works. In almost all models, this is a polypropylene body, which has a filler neck with a cap at the top and two nozzles, upper and lower. The lower valves are connected to the cooling system line, and the upper ones drain excess vapors and air bubbles.

In modern cars, the design of the expansion tank is supplemented with float sensors that monitor the coolant level. To do this, there is another neck in the case where the sensors are installed.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

There are several checkboxes on the side of the container:

  • lower risk – min;
  • higher risk – max.

The fluid level should be somewhere in between.

How expansion tank works

Now it is worth touching the work of the tank. To begin with, it is worthwhile to give the values ​​u200bu200bof the boiling point of various liquids (at atmospheric pressure):

  • water – 100°С;
  • antifreeze – 105-110 ° C;
  • antifreeze – 120 ° C.

Now you understand why most drivers prefer to buy antifreeze. Considering the question of how to check the cap of the VAZ 2114 expansion tank (for example), it is worth delving a little into the theory. The boiling point of the coolant can be additionally increased by increasing the pressure above atmospheric. For this reason, the entire system is reliably sealed to maintain the desired pressure level. The optimal value is 1.1-1.5 atmospheres.

However, even a high level of vacuum (0.03-0.1 kg / cm²) does not help a running engine. This may cause air to leak into the cooling system, resulting in air pockets. As a result, fluid circulation will be hindered, which will eventually lead to overheating of the engine.

The role of the tank cap

Now we know what an expansion tank is for. But here a very interesting question may arise, what role is assigned to its cover? Above, a dangerous situation has been described that can occur with a strong vacuum.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

Many drivers, especially beginners, do not know how to check the expansion tank cap on a VAZ. It goes without saying that they believe that it only works as a shut-off device and does not allow coolant to splash out while the car is moving. This is partly true and this element really works as a locking device. However, he has a much more important task.

As you know, the pressure in the cooling system should be kept at 1.1-1.5 atmospheres. The cover copes with this task with a bang. How do you do this? The fact is that his device has two valves:

  • security;
  • empty.

The first looks like a spring-loaded rubber diaphragm that is pressed in from the outside. The second is a rubber washer with a small spring hidden inside a large one.

At normal system pressure, both valves are closed. The tank is sealed, so as the temperature of the coolant rises, so does the pressure. As soon as it exceeds the permissible value, the safety valve opens and part of the air vapor is thrown out.

As the car cools down, the volume of liquid in the system decreases, and due to the tightness itself, a vacuum occurs. This is where another valve comes into play: the vacuum valve. When opening, the pressure in the system is compared with the atmospheric value.

Location of the Republic of Belarus

To check the expansion tank cap valve, you need to know where it is, which is difficult for some beginners. If we take into account the domestic transport of the largest manufacturer AvtoVAZ, then depending on the specific model, it can be located in different places.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

For example, in the VAZ-2110-12 line, the tank is located on the driver’s side (in relation to the movement of the car) between the shock absorber strut and the interior partition. In VAZ-2114-15 models, the container is also located on the left side, but is located behind the trunk glass. Around the same place is the fuel tank of the Audi 80.

Symptoms of a failed tank cap

All devices fail sooner or later, no matter how simple or complex they may be. The expansion tank cap is no exception. Only the whole difficulty lies in the problematic diagnosis of his condition. And the consequences of his break can be very serious.

How to check the operation of the expansion tank cap? But what is much more important: what can lead to the diagnosis of this detail? In fact, the presence of the following signs:

  • Smoke is visible from under the hood.
  • Motor overheating.

Smoke may come out of the fluid entering the hot intake manifold. At the same time, the engine temperature is within normal limits. This problem is relevant with a faulty valve that opens earlier than necessary. For this reason, splashes of coolant occur.

Often the cause of overheating is a broken low pressure valve. Due to its poor performance, congestion forms in the cooling system, which leads to such a sad result.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

In addition, signs can be considered a rupture of the clamps, as well as a breakdown of the radiator, pipes or other elements of the system, including the tank itself. All this indicates the need to check the expansion tank cap (VAZ 2114 or another car) and replace it in case of a malfunction.

Verification procedure

It is not so easy to check the operation of the tank cap, since it is necessary to create pressure, which is difficult. Service centers use special devices with a pump and pressure gauge. This allows you to set the exact values ​​for the actuation of the hood valves. Self-diagnosis can be carried out, only it is less accurate in relation to the result. However, the item will be defective.

First you need to unscrew the cover on a cold engine and inspect it: are there any cracks, chips, dents, broken sealing elements, abrasions and other defects. If the result is positive, it is worth moving on to the next method, for example, checking the expansion tank cap. Just screw up first.

Now you need to start the engine and wait for it to warm up to operating temperature. Then you need to start slowly unscrewing the lid. If you hear the sound of escaping air, similar to unscrewing the cap from a soda bottle, then everything is in order – the part is working properly and holding pressure in the system. While the engine is still running, it is worth inspecting the thick pipes for dents. If yes, then one of the valves is not doing its job.

How to check the expansion tank cap. The device and principle of operation of the expansion tank

How to check the expansion tank cap differently? You can also do this (preferably even with a cold engine): unscrew the cap, then squeeze the thick tube with your hand, and then screw it into place. Now you can remove your hand and observe: the tube takes its original shape – everything is in order, otherwise it is better to replace the cap. Only this method cannot always be used due to the design features of the power unit of different cars and the location of the nozzles.


It is worth paying close attention not only to the expansion tank itself, but also to its cap. Periodically evaluate your condition to avoid serious consequences. Also, do not neglect the maintenance of the car in relation to the cooling system. That is, check the level of coolant in the tank, topping up if necessary. And change antifreeze in time, which will allow you to enjoy driving a car.

Each driver needs not only to know how to check the expansion tank cap, but also to understand how it works. This will teach you to be more responsible about your vehicle and save the family budget.

Post source: wekauto.ru

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