How to test engine cooling system

In this article, mechanical girl shows us how to test the cooling system of an engine and its possible failures. In this case for a Toyota Starlet.

Test engine Cooling System

Hello such, today I come with another article on how to attack an overheating failure of an engine, in this case that of a Toyota Starlet.

There are usually only two refrigeration systems in the petrol engines at the moment, these are the open system, and the closed one. Although they have some differences, the conditions necessary for them to work correctly are practically the same. So here I describe some things to consider when you review this system:

It is important to clarify that these procedures described here are valid for cars that do not have a computer.

As we always start testing and discarding from the simplest to the most complicated.

Check the lid that maintains the system pressure

It is very important that the refrigeration system maintain the pressure and more when it is a closed type system.

Remove the lid (with the engine cold) and inspect that the gums are well, have no signs of fracture or are overdue, as the spring is not corroded or badly positioned.

How to do the test?

One would be to run the engine until hot, at no time should you throw water through the edges of the lid, nor should it leak water if there are no signs of motor overheating (bubbling or hoses).

Find water leaks in the system

As mentioned above, the system must be airtight and water leakage is the most common problem, especially in cars over 5 years in service.

Check that there are no water spots in hose joints, or broken pipes where the refrigerant can escape. You have to be very meticulous about this because usually leaks are where less is visible. lol.

How to do the test?

The engine is usually run for a few minutes and then turned off. At this time the system takes pressure and is when the leaks begin.

If the liquid leak is moderate it is possible to see the dripping under the engine, in these cases it is only enough to follow the drip until it starts in the engine.

It is necessary to pay special attention in cars equipped with heating, because also there circulates the refrigerant of the engine and it is possible that there are leaks.

Check electrical fan CONTROL system:

They usually have two, one for the instrument panel and the other for the control of the electric fans. With a multimeter that measures resistance it is possible to discard which is which, you only have to measure the resistance of the sensor with respect to ground. For the one that goes to the instrument panel will give resistance greater than 90 ohm (cold tank at ambient temperature 25 º C). For the one that goes to the control of the Electros will give us or 0 ohm or infinite resistance.

In the video I did both to see how the sensors and their actuators are in this case, the board water and the ignition of the electro.

How to do the test?

For this type of vehicle is quite simple, only enough to ground the cable that connects to the sensor, this way it is told the system that the car is overheated.

Important, if it is an electro (reverse) control sensor, when the connector is removed, the fans will be pulled out and when they are terrified, they turn off. Keep this in mind when doing the tests.

Check the thermostat

The thermostat is responsible for maintaining the optimum temperature of the engine, opening or closing an internal vane that it brings. When the spring becomes clogged or damaged, it tends to remain closed by overheating the motor. The thermostat is always at the engine water outlet.


How is the test performed?

This is already a test of greater skill, usually consists of starting the engine and touching the refrigerant inlet and outlet hoses of the radiator. When the engine is cold both hoses are at the same temperature, when the motor heats both hoses have different temperatures than the touch, this is because when the thermostat opens, the radiator starts its work, cooling the water, and then this is why The temperature difference in the water flow. Eye, this is a fairly empirical test and needs experience to carry it out.

The best of all is to remove the thermostat and test it in hot and cold water. But in this case it is already a major task.

Water Pump Problems

The water pump is the heart of the system, it is the one that moves the fluid inside the machine. Its most common problem is the leakage by the central axis, very rarely it is by obstruction.

How to do the test?

In my opinion it is better to dismantle it, if all other tests fail. It is usually possible to see the fluid move if the radiator cap is removed and it is not full, but it is a very empirical test, and we would not be seeing the pumping efficiency.

Here I leave a video of how I did these tests in a Toyota Starlet.


Do you have questions or doubts?

Questions or suggestions can use the form below and I will gladly answer them.

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Written by Dennis García.

Mechanical Girl



Como siempre, me encanta

Muy bueno el artículo Dennis. Sigo tus videos y tus artículos.



    Sin duda imperdible, muy buenas recomendaciones.

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      How to test engine cooling system

      How to test engine cooling system

      In this article, mechanical girl shows us how to test the cooling system of an engine and its possible failures. In this case for a Toyota Starlet.

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      • Asked by Martin Rodriguez
        on 08/18/2018
        Caramba, aprendí algo nuevo. El sistema de enfriamiento Cerrado y el Abierto. ¿La prueba al electroventilador para los carros nuevos como seria? Answer:
        Bueno Martin, para probar los electros de los carros nuevos es muy sencillo. Solo debes de encender el motor y sacar el conector del sensor de temperatura. El ECT, con eso encenderá la luz de motor o en su defecto el foco de temperatura y arrancarán los electros en alta velocidad. Al volver a conectar, todo quedará como antes. Si no encienden con esta prueba, hay un problema en el circuito.
      • Asked by Hector
        on 10/02/2018
        Buenos dias chica, te felicito de verdad ppr tus conocimientos. Mi cas: acabo de anillar el motor y al encenderlo no aguanta el minimo y ademas burbujea aire por el radiador... que estara pasando? Answer:
        Que tal Hector, muchas gracias por la felicitacion. ; ) ¿Burbujea por el radiador? ¿Apretaron bien con el torque correcto las empacaduras de la cámara? ¿Hay aceite en refrigerante? o agua en el aceite del motor?

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