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Basics of Coolants

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Basics of Coolants


Coolants-Coolants (or antifreeze) are basically heat transfer fluids which are used to transfer unwanted heat energy from engine to radiator. Coolants protect system from corrosion and to prevent the freezing of radiator cooling media.

Need of Coolants -. In a automotive engine, only one-third of the total energy produced works to propel the vehicle forward. An additional one-third is removed as heat energy by the exhaust system. The remaining one-third of heat energy produced is taken away by the coolant.

Application of Coolants- Coolant is widely used in automotive and heat transfer applications. Some of the other applications are cooling systems of automotive engine, stationary & marine diesel engines, as a secondary refrigerant, in air conditioning systems,etc.

Engine cooling system- The engine block of liquid-cooled engines contains passageways or water jackets that the engine coolant passes through. The coolant moving through the engine block removes heat from the engine. The coolant then carries the heat it removes back to the radiator through a system of hoses. In the radiator, heat is rejected from the coolant into the atmosphere, with the help of air flow through the radiator. The air flow is aided by forward movement of the vehicle and by a fan which draws air through the radiator, whether the vehicle is moving or stationary.. Coolant is then circulated from the radiator outlet tank through the water pump and into the cylinder block to complete the circuit. Coolant expands as the temperature and pressure rise in the cooling system. When the limiting system working pressure is reached, the pressure relief valve in pressure relief cap is lifted from its seat and allows coolant to flow through the radiator overflow hose into the radiator coolant recovery reservoir. The pressure relief cap has a rubber seal on the underside to prevent leakage. When cooling system temperature and pressure drop, the coolant contracts in volume, reducing pressure in the radiator. Coolant in the radiator coolant recovery reservoir will then flow back into radiator though the vacuum relief valve in the pressure relief cap. The constant control relay module (CCRM) activates the cooling fan motor when coolant or engine reaches a specified temperature. On vehicles equipped with air conditioning, the cooling fan motor is activated whenever the A/C clutch is engaged.


Coolant Composition- There is three components that form coolants. These components are ethylene glycol or propylene glycol, de ionized water and corrosion inhibitor. Ethylene glycols about more than 90%, corrosion inhibitors are used about less than 5%.

Ethylene glycol  -Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound  widely used as an automotive coolants (or antifreeze) and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid. Ethylene glycol is toxic, and ingestion can result in death.

Due to its low freezing point ethylene glycol resists freezing. Pure ethylene glycol having a much higher boiling point and lower vapor pressure  than pure water. Ethylene glycol not only depresses the freezing point, but also elevates the boiling point such that the operating range for the heat transfer fluid is broadened on both ends of the temperature scale.







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