Engine radiator cap, Water jacket and Antifreeze mixtures

Radiator pressure cap: 

Water subjected to atmospheric pressure boils at 100*c. When the cooling system is pressurized, the increase in boiling point enables the engine to operate at a higher temperature with the result that power, economy and engine life are all improved. The operating pressure of system is controlled by the radiator cap. The following precautions should be taken when removing radiator caps. If the engine is hot:
➤ Protect the hand with a heat-resistant glove
➤ Remove the cap slowly to allow the pressure to release before the cap is detached
➤ The water may boil when the cap is removed.

The pressure radiator cap is fitted in the filler neck portion of radiator top tank. It has two valves:
➤ Pressure Valve: In case pressure rises, components of the cooling system are likely to be damaged. In order to avoid this, a pressure valve is provided. It is spring-loaded and releases the excess pressure.
➤ Vacuum Valve: When the engine cools, the pressure of the system decreases. This happens due to loss of coolant and this creates vacuum. At this time, the vacuum valve opens and allows the air to enter.

 Water Jacket:
 Water jackets are provided in the cylinder block and the cylinder head. Cold water from the radiator flows through water jackets. This water carries the heat from these hot parts to the radiator.

 Antifreeze mixtures:
There is little chance of pump-circulating water in the cooling system of a modern car freezing while the car is in operation, but there is every chance of such freezing when the car is parked and the atmospheric temperature is below freezing. When this occurs, the expansion may cause the water jackets pipes or radiator to break. To prevent freezing, an anti-freeze solution is added to water. It lowers the temperature at which freezing of the coolant occurs. Most modern anti-freeze solutions contain special chemical additives called inhibitors to reduce corrosion of the metal parts. Care should be taken to avoid splashing anti-freeze on the vehicle paintwork of the metal parts, since some of the chemicals can soften the paint. The ideal requirements for an anti-freeze mixture are:

* Should not be harmful to any part of the cooling system.
* Should be easily dissolved in or combined with water.
* Should be cheap.
* Should not waste by vaporization.
* Should not deposit any foreign matter in the jackets or pipes.
Antifreeze is mixed with water to make the coolant for the engine. In addition to providing freeze and boil protection, properly formulated antifreeze protects the engine components and radiator from corrosion. Make sure that you use a 50/50 mixture of antifreeze and water. Pure antifreeze will not conduct heat and cause the engine to overheat. Water is very key ingredient to this mixture. Water heavy with mineral salts will cause engine scaling and reduce the ability of the engine to transfer heat and will ultimately contribute to premature failure. Scale can from on water pump seal surfaces causing the pump to fail. It is critical that all cooling system heat exchange surfaces remain clean. Hard water scale can block a cooling system's ability to transfer heat resulting in overheating. Only 1.6 mm of scale will reduce cooling system heat transfer efficiency by 40%. Finally, remember most antifreeze contains ethylene glycol, a poisonous chemical. Always keep both new and waste antifreeze in tight containers and store them carefully so that pets and more importantly children will not get into them.