Logo carsalmanac.com

Antifreeze boils in the expansion tank: the main reasons for what needs to be done

Table of contents:

Antifreeze boils in the expansion tank: the main reasons for what needs to be done
Antifreeze boils in the expansion tank: the main reasons for what needs to be done

There are a whole host of reasons why coolant may boil. But often the problem can be fixed on its own. As practice shows, in most cases the driver himself is to blame. After all, the cooling system must be serviced regularly. Let's take a closer look at why antifreeze boils in the expansion tank, and how to fix the problem.

boiling antifreeze in expansion tank
boiling antifreeze in expansion tank

Engine cooling system

First of all, I would like to understand in more detail how the engine is cooled. The system as a whole is not complicated, but there are some nuances in its operation. It must be understood that as soon as you start the car engine, it heats up intensely. It has special channels through which coolant circulates under pressure and removes part of the heat. The main elements of the cooling system: radiators, pump, thermostat, expansion tank cap(air valve), nozzles, etc.

The boiling point of antifreeze is greater than that of water. That is why it is used in modern cars. If we recall the course of physics, we can conclude that an increase in pressure leads to an increase in the boiling point. Accordingly, the higher the pressure, the higher the temperature at which the coolant will boil. But heavy operating modes (for example, standing in traffic jams) inevitably lead to a constant increase in pressure in the system. When it reaches a certain value, the air valve opens, thereby venting excess steam into the atmosphere.

coolant level in expansion tank
coolant level in expansion tank

About regular maintenance

As noted at the very beginning of this article, the cooling system must be periodically checked for leaks, the condition of the antifreeze, the performance of the pump and thermostat. If this is not done, then there is a possibility of serious damage and overheating of the engine. Overhaul is not a cheap event, so you should not bring it to this.

Another rather important point is the service life of antifreeze. Much depends on its type. For example, it is desirable to change G11 every few years, and G12 + can easily withstand about 5 years. At the same time, there are manufacturer's recommendations for the type of coolant and the regularity of its replacement. Therefore, if you notice that antifreeze periodically boils in the expansion tank, then this does not indicate any mechanical malfunction. It is possible that he simply lost some of his performance, which is whythe boiling point has dropped. Well, now let's go directly to the main problems and methods for their elimination.

Insufficient level of antifreeze in the expansion tank

When there is not enough coolant in the system, the boiling point drops. In most cases, the problem is solved by regular topping up. It is advisable to do it cold. This is due to the fact that at high temperatures the liquid expands. Therefore, if you fill in the expansion tank to the "minimum" mark, when the system cools down, the antifreeze will become much less.

squeezes antifreeze out of the expansion tank
squeezes antifreeze out of the expansion tank

Actually, there is nothing complicated in topping up. We find the expansion tank and unscrew the plug. It can be either ordinary plastic, which performs almost no function, or airtight. After we unscrewed it, fill in the required amount of antifreeze. It is desirable that the level of antifreeze in the expansion tank be between the "maximum" and "minimum" marks. As for the reasons due to which the level fell, there are only a few of them. It is likely that during the maintenance of the system, antifreeze was not added. The second option is a leak.

Thermostat failure

If you notice that the antifreeze is squeezing out of the expansion tank, then this may indicate a jammed thermostat. The fact is that it works like a valve and has two positions: closed and open. In the closed position, circulation through the system is carried out in a small circle. In a large circle, the liquid passes through the radiator, whichcontributes to its rapid cooling. If the car engine is cold, the thermostat valve is closed, which contributes to the accelerated heating of the power unit. When the engine is hot, the thermostat opens and the coolant circulates through the radiators, where it is cooled by oncoming air flow or diffusers.

What do we get if the thermostat gets stuck? There are two options: the antifreeze is constantly boiling in the hot expansion tank. This is due to improper coolant circulation. At the same time, it squeezes the antifreeze out of the expansion tank, as it constantly expands. This indicates that the valve is stuck in the closed position. The second option is that the car will warm up for a very long time. For any problems with the thermostat, it must be replaced, it is not too expensive to save on such a critical part.

how to add antifreeze
how to add antifreeze

Cooling radiator and its malfunctions

Designers at the stage of creating a car lay down certain data on the speed of movement of antifreeze in the system. Over time, the interior of the radiator becomes clogged with s alt and sediment. This cannot be avoided, although the problem is quite simply eliminated on its own. It is enough to flush the system with special means when replacing the coolant, which will partially or completely remove the sediment formed during operation. As a result, the coolant will circulate faster and cool much more efficiently.

At the same time, do not forget about the radiator outside. Since it is installed behind the front bumper and is cooled by the flowoncoming air, it becomes polluted from the outside quickly enough. Honeycombs are clogged and heat transfer is disturbed. Air does not pass through the radiator, which leads to the boiling of antifreeze in the expansion tank. Honeycombs are cleaned with special washing solutions under low pressure. It is advisable not to use a car wash, because you can bend the honeycomb.

Air valve failure

As we have already figured out, the expansion tank cap is a rather important element, although many motorists do not change it over the entire life of the car. But here, whoever is lucky, because the valve can work properly for quite a long time, or it can fail in a year of operation or even less.

Checking the cork for performance is quite simple. To do this, you need to start the car engine and warm it up completely. When excess pressure builds up in the system, the valve should work and the excess pressure will be released. You can understand this by the characteristic sound. In addition, a valve failure will cause antifreeze to be squeezed into the expansion tank. The cover is beyond repair and must be replaced.

why does antifreeze boil
why does antifreeze boil

Cooling fans

The antifreeze temperature sensor is needed not only to monitor the status of the system on the dashboard. It performs another, no less important function. The sensor sends data to the on-board computer and, when a certain temperature is reached, gives a signal to start the cooling fans. If diffusers are practically not needed when driving at high speed, then intraffic jams, they are a must.

If something is not working properly, then the fans do not start, and often the sensor itself works fine. The problem may be an open circuit or a blown fuse. You can ring the wiring both on your own and with an electrician at the service station. After that, the problem should disappear. But first of all, it is advisable to check the fuse. To do this, just install a new one. The relay is the least likely to fail. For some car models, it cannot be bought at a regular car dealership. In this case, as a temporary solution, you can install a jumper. But you need to understand that the fan will run constantly.

Break in the system

Antifreeze leak is the most common problem. Over time, the pipes dry out, microcracks appear on them. The attachment points to the radiators and expansion tank are also weakened. As a result of this, at first a small leak appears, which only intensifies over time. If the problem is not fixed, then eventually the pipe may break. All antifreeze will spill out and the engine will overheat if not noticed in time.

antifreeze leak
antifreeze leak

To prevent this from happening, it is recommended to periodically change the rubber pipes, inspect the condition of the fasteners, etc. Leakage may also occur as a result of a malfunctioning air valve. When there was too much pressure in the system, a weak spot was found through which the coolant leaves. In this case, it is not clear how much antifreeze to fill in, because its level willconstantly change. It is advisable to fix the leak as soon as possible.

Water pump

The so-called pump is responsible for pumping coolant through the system. Usually the water pump is included in the gas distribution mechanism and changes according to the regulations. Therefore, it is advisable to install a new pump every 70-100 thousand kilometers in order to avoid problems.

But it happens that there is not enough money for the original pump. In this case, drivers buy an alternative, most often a Chinese substitute, and then wonder why antifreeze boils. After some time, the pump leaks, which can lead to the destruction of its impeller and the ingress of plastic elements into the systems of the power unit. Replacing a failed pump is not cheap, but it needs to be done as soon as possible. It is not recommended to travel by car on your own in this case. Cheaper to pay for a tow truck.

A few tips for motorists

So we figured out the main reasons for boiling and squeezing out antifreeze. As you can see, there are a huge number of them. Often, identifying and fixing the problem is quite simple. But still, it is necessary to follow a number of simple rules that help to always maintain the engine cooling system in good condition:

  • regular replacement of antifreeze;
  • checking the thermostat and air valve;
  • cleaning the radiator outside and inside when replacing antifreeze;
  • inspection of nozzles for defects in the form of cracks;
  • replacement of the pump along with the timing kit.

Actually, nothingcomplicated, as well as adding antifreeze to the system. But at the same time, failure to follow the manufacturer's recommendations can lead to more serious problems.

how much antifreeze to fill
how much antifreeze to fill


When the car engine overheats, the power unit may not fail. It all depends on the duration of the ride at elevated temperatures and the design features of the motor. For example, an internal combustion engine with an aluminum block is more afraid of overheating than others. Therefore, such a motor most often jams when a critical temperature is reached.

Many motorists know how to add antifreeze, but this does not save them from problems. After all, you can miss the level sooner or later. As practice shows, serious breakdowns happen at the most inopportune moment. A pipe can break on a highway far from home, and even the plug of the expansion tank does not give any guarantee. What to do in this case? The main thing is not to panic. If the motor was not overheated, then serious consequences have already been avoided.

To avoid such troubles, it is necessary to follow the manufacturer's recommendations. It is advisable to buy only original spare parts, because in 90% of cases they are of the highest quality. So you know why antifreeze boils in the expansion tank, and what to do if such a problem occurs.

Popular topic