To check the thermostat (without removing it from the car), you just need to understand the principle of operation of the car engine cooling system. Disassembly of the assembly, as a rule, is only necessary in order to finally verify the diagnosis and perform repairs. The minimum that is required for diagnostics is an understanding of the node device. The maximum is a multimeter (complete with a thermocouple), a pyrometer and a pot of water that can be heated.

Where is the thermostat located in the car

The thermostat is a simple valve assembly that separates the circuits of the car's engine cooling system. At the same time, it works automatically, depending on the current heating or cooling of the coolant. The small circuit is the "shirt" of the engine and the radiator built into the cabin, which acts as a stove. The large contour is all of the above plus a cooling radiator in the front of the engine compartment.

The thermostat is installed on cars so that it is possible to “connect” the main cooling radiator to the small ring. When the power unit heats up under load, the valve gradually opens slightly, and through it part of the hot coolant is discharged into the radiator. There it cools and enters again into the small ring. In order for the motor to be operated in the most optimal thermal regime for it, the valve maintains operating parameters by opening and closing slightly as needed.

To find an element under the hood, the easiest way is to start from the main radiator. From it comes a large section pipe. Since there are two of them coming out of the radiator, we need the one above. The thermostat itself is usually located in an aluminum housing or directly on the engine itself, where the upper pipe from the main radiator fits. The element itself can be seen only after partial disassembly (including the need to drain the liquid) of the cooling system.

Node malfunction symptoms

Breakdowns can be conditionally divided into two groups - non-critical and dangerous.

Non-critical breakdowns

This includes faults such as:

  • jamming in the open state;
  • early opening;
  • incomplete closure.

The result of such breakdowns will be a violation of the thermal regime of the motor without fatal consequences. It will not be able to warm up quickly, while in cold weather it will not enter the operating mode at all. The stove will blow cool or barely warm air. There may also be a decrease in the power of the power unit and increased consumption. Unpleasant, but you can ride.

Dangerous breakdowns

These include:

  • jamming in a fully closed position;
  • late opening;
  • early closing;
  • incomplete opening.

The last three can lead to the fact that the motor will often run in an overheated state. Complete jamming of the element in a completely closed position is almost guaranteed to end in critical overheating and serious damage. This is the most dangerous malfunction of the cooling system, except for depressurization.

How to check if it works

There are several ways to check the health of the valve at home. Consider the main 7.

Method number 1. Engine warm-up time to normal operating temperature

The most important function of the valve is to reduce the warm-up time of the power unit, which has stood idle for a long time. This is especially true in winter. A cold car drives badly, and it is uncomfortable to be in the cabin. Not to mention the icy glass, through which you can not see the environment on the road.

This function is performed simply - when the engine is cold, the valve is completely closed. The coolant pumps around in a small circle and warms up quickly. At the same time, it does not enter the large radiator, due to which thermal energy, which is precious in this mode, is not lost. This function allows you to quickly start moving in the cold season - the engine will start to work stably and economically earlier, the stove will blow warm, the windows will become transparent.

If the power unit warms up for too long, then this is a sign of a valve stuck in the open or slightly ajar position. The heated coolant simply “runs away” into the main radiator, being dumped into a small cold circuit. When the car is standing still, that is, the radiator is not blown by oncoming air, it is somehow still possible to warm up the engine with such a breakdown. But as soon as you start moving, the heating in the small ring drops, and the stove starts to blow cold.

It is worth noting that diesel engines, even with a working unit, warm up much longer than gasoline ones. It must be taken into account that in this case, that with other methods of checking the cooling system.

Method number 2. Behavior of the arrow °t when the engine is running

In any car, a simple coolant temperature indicator is provided on the panel in front of the driver. It can be both pointer and digital. Watching it with the engine running, you can quite accurately determine the faulty thermostat.

On a serviceable gasoline engine, the pointer behaves approximately as follows:

  1. After a couple of minutes of running a cold engine, the arrow begins to rise.
  2. After 5-10 minutes (depending on the car and the weather outside), the pointer reaches the largest sector, indicating the operating range.
  3. When driving without load, the needle may oscillate slightly.
  4. With the advent of a serious load, the pointer rises to a certain point, after which it drops quite quickly.
  5. If the load is constant, and it’s hot outside, the arrow is near the “red zone” and forced airflow is turned on.

If, after several minutes of operation of a cold power unit, the arrow does not move away, then there is a possibility that the element “passes” the heated coolant into a large circuit. This means that it is either stuck in the fully open or partially open position. If in the parking lot the arrow reluctantly, but rose, and immediately went down sharply at the beginning of the movement, the valve definitely “does not hold”. The radiator begins to be blown by a stream of oncoming air, cooling the entire coolant.

If the coolant temperature gauge moves very quickly into the “red zone” and does not leave it even when the fan is running, the element is likely to be in a completely closed state. With this behavior of the arrow, you need to immediately turn off the engine and find out the cause of overheating.

Method number 3. Approximate measurement of current °t

This simple method allows you to check the thermostat without any tools and devices, and without disassembly. The test is carried out on a cold engine, that is, when the car has been idle for several hours. In no case do not touch the pipes of the cooling system on a running engine - this can result in burns to the skin of the hands.

Before checking under the hood, you need to find two pipes. The first is between the node in question and the main radiator. Finding it is the easiest. It is usually the thickest, and runs from the engine to the top of the radiator. The second must be sought from the opposite side of the node in question. In extreme cases, you can gently touch the motor itself. But only as described below.

Checking principle:

  1. Let the motor cool down completely.
  2. Run it and immediately go to the hood.
  3. Grab the small ring tube (or feel your shirt) with one hand and the one that goes to the top of the main radiator with the other.
  4. First, you should feel how the coolant warms up in a small circuit (if you touch the engine, then do not do this for a long time).
  5. The branch pipe of the large ring (to the radiator) must remain cold at the same time.
  6. Release the small circuit nozzle when it becomes hot.
  7. Wait until the circuit nozzle feels warm and release it too.

If immediately after starting both pipes warm up evenly, the valve is either constantly open or ajar. That is, it is jammed and it is faulty. If the motor began to overheat, and you did not wait for the heat in the large circuit pipe, the valve stuck in the fully closed position.

It should be emphasized that this method of testing is dangerous for your health. It is best to stop touching the nozzles immediately after the temperature difference (or equality) between the small and large circuits has been established. For a more accurate check, there are less traumatic ways.

Method number 4. Precise measurement of the actual coolant temperature

To check this method, you will need a device that measures temperature up to +150 degrees Celsius. The easiest way is to use a multimeter with a thermocouple (preferably two at once). A pyrometer will also work. One is enough.

The principle of verification is as follows:

  1. Give the engine time to cool down.
  2. Run it and measure the temperature of antifreeze in both circuits.
  3. If you are doing this with a multimeter, alternately apply the thermocouple to the small ring nozzle, and then the large one.
  4. If you have a pyrometer, then just point its nozzles one by one, comparing their temperature.
  5. Let the engine warm up, constantly monitoring the thermometer readings.

If the temperature of both circuits is the same during the entire test, the valve is ajar (or stuck open). When it is normal, the temperature of the small ring will rise rapidly, and in the large one, the liquid will remain cold for some time. After warming up the power unit, the indicators on the pipe going to the radiator will slowly creep up. This indicates that the thermostat is working properly, gradually opening slightly, bleeding hot antifreeze into the radiator.

Method number 5. Valve testing by heating in water

This is the most visual and accurate method, the implementation of which will require:

  • a saucepan with water;
  • gas or electric stove;
  • submersible thermometer for measuring water temperature.

To check the valve in this way, it will need to be removed from the cooling system. To do this, you will have to at least partially drain the coolant through the drain plug provided at the bottom of the radiator. Drain 2-3 liters of antifreeze, remove the thermostat. Usually, to do this, you need to remove the pipe going to the radiator and unscrew 3-4 bolts on the body.

The removed part should first be inspected visually. If it is in an open state, then it can be thrown away and not checked further. He is obviously wrong. If everything is in order, find the numbers on it - they indicate the temperature range of operation of this particular model.

The thermostat to be tested must be fixed in a prepared container with water, following two rules. First, it must be in the liquid all. Secondly, he should not touch the walls and bottom of the container. According to the same rules, a thermometer must be placed in the container.

When everything is prepared, heat the water, constantly monitoring the behavior of the plate and the thermometer readings. Upon reaching the lower temperature threshold indicated on the body, the plate should begin to open slightly. When the water warms up to the upper threshold, the thermostat should open completely. If it doesn't, it's defective. It is also unacceptable that the plate began to move in slightly heated water, as this will indicate too early opening.

Next, you need to stop heating, continuing to monitor the thermostat and thermometer. When the water cools to the upper limit indicated on the body, the valve should begin to close. At the lower threshold, it will close completely. If not, a replacement part.

Method number 6. Incomplete actuation

When checking in boiling water, you also need to pay attention to the fact that the valve opens and closes completely. If it only partially opens, and the water has been boiling for a long time, then on a car this can lead to overheating of the engine. The throughput of a valve that is not fully open is simply not enough to pass a lot of overheated coolant through the radiator.

Also, after cooling, the valve disc should close tightly.

Method number 7. Late or early firing

It is also determined when checking in boiling water. To do this, you need to compare the temperatures indicated on the case with the actual readings of the thermometer at the time of the start of opening and full opening. If there is an upward shift, then for the engine this means regular operation with overheating. Sometimes critical. If the thermometer shows less than what is written on the case, the motor will never work in optimal temperature conditions for it.

VIDEO: test thermostat


Checking the thermostat on a car is a simple and necessary procedure that can be performed without removing it from the car. Disassembly is usually required only for more accurate diagnosis or repair. It is necessary to check the thermostat immediately, as soon as symptoms appear that indicate its malfunction - the engine heats up for a long time (it does not warm up at all in winter), the stove blows cold, the temperature in the cooling system drops sharply when the movement starts. A particularly dangerous symptom is overheating of the engine.

If you are not sure about the operability of the node, but do not want to check it yourself, contact a specialist.