The function of the automobile cooling system is to dissipate the heat of the engine in time, so that the engine works at the most suitable temperature. The ideal automobile cooling system should not only meet the needs of the engine cooling, but also reduce heat loss and energy consumption, so that the engine has better energy saving effect on the basis of ensuring good power performance.

I. Working principle of cooling system

Cooling system plays a very important role in the automobile, the engine cooling system generally adopts water cooling cooling, the typical cooling system is composed of radiator, radiator hose, thermostat, water pump, cooling fan and fan belt.

It relies on a cooling water pump that flows through the oil cooler, crankcase cooling water jacket and into the cylinder head, taking excess engine heat away.

Major circulation: when the engine is working under normal thermal conditions, that is, water temperature is higher than 80℃, cooling water should all flow through the radiator to form a major circulation. The main valve of the thermostat is fully open and the secondary valve is fully closed.

Small circulation: when the cooling water temperature is below 70℃, the steam pressure in the expansion box is very small, and the cooling water does not flow through the radiator, but only carries out small circulation between the water jacket and the pump.

Two, the role of coolant

The coolant plays a very important role in the normal operation of the engine. Too high or too low temperature of the coolant will adversely affect the operation of the engine. If the temperature of engine coolant is too high and the viscosity of lubricating oil is reduced, the friction loss of engine components will be intensified.

If the engine coolant temperature is too low, the viscosity of lubricating oil increases and the fluidity becomes poor, which is also not conducive to lubrication, thus reducing the power output of the engine and affecting the mechanical efficiency of the engine.

Coolant is the heat transfer medium in the cooling system, with cooling, anti-corrosion, anti-scale and anti-freezing and other functions, it is composed of water, antifreeze and various additives.

1. Water is an important part of the coolant. It has a large specific heat capacity and fast heat conduction, and the heat absorbed by water is easy to emit.

2. Antifreeze is to reduce the freezing point of coolant. Because of the high freezing point of water, it is easy to freeze when used in cold and low temperature weather.

3. Other additives

Additives generally not more than 5%, mainly corrosion inhibitor, buffer, anti – scale agent, antifoaming agent and colorant.

(1) Corrosion inhibitor: it can effectively prevent the corrosion of metal substances in the cooling system, because the cooling pipeline is mainly composed of metal parts, and the cooling system is prone to corrosion and damage under the condition of high pressure, heat load and corrosive medium.

(2) Scale inhibitor: it can effectively remove scale and improve heat dissipation capacity. During the use of coolant, scale is often formed on the inner surface of the cooling system. The thermal conductivity of scale is lower than that of metal, which seriously affects normal heat dissipation.

(3) antifoaming agent: can effectively prevent foaming, coolant in the pump at high speed under the forced circulation, usually produce foam, a lot of foam not only affect the heat transfer efficiency, but also aggravate the cavitation corrosion of the pump.

(4) colorant: in the process of using coolant, it is generally required to add a certain colorant, so that the coolant has a striking color. In this way, when the cooling system fails, the location of leakage can be easily determined by observing the external pipeline of the cooling system.

Three, the classification of coolant

Engine coolant is divided into glycol coolant and propylene glycol coolant according to antifreeze:

1, ethylene glycol specific heat capacity, thermal conductivity, viscosity and boiling point are important parameters that affect the heat transfer performance of ethylene glycol aqueous solution. The specific heat capacity and thermal conductivity of ethylene glycol aqueous solution decrease with the increase of concentration, and the viscosity increases with the increase of concentration.

2, propylene glycol in reducing freezing point performance and glycol is basically the same, but also less toxic than glycol, the price is more expensive than glycol.

Four, cooling system maintenance

1. Selection of coolant

(1) In order to prevent the cooling system from freezing, appropriate antifreeze can be selected. Generally, the freezing point of antifreeze should be 5℃ lower than the lowest temperature in the area.

(2) Different types of antifreeze can not be mixed.

2. Replacement period and usage

(1) Replacement cycle: Coolant should be replaced once every 2-3 years, according to the operation manual.

(2) Adding amount: Antifreeze should be added to the expansion tank between F (MAX) and L (MIN) marks in the cooling state of the engine.

3. Daily maintenance:

(1) Daily attention should be paid to observation, once there is insufficient coolant, white signs on the surface of the water pipe or white milk in the oil, it is the leakage of coolant.

(2) Check the connection position and state of all cooling system hoses and heater hoses. If there is expansion or deterioration, please replace it in time.

Summary: Cooling system plays a very important role in the car. In daily use, it should be maintained frequently, so as to nip in the wind and keep the car in a good state. It should be checked regularly whether the engine coolant is sufficient, and appropriate coolant should be added or replaced in time when needed