Radiator cap for your car

The radiator cap is a small, though important component of the cooling cycle, sealing the car's radiator at the top. It can easily be removed in order to replenish the cooling water. Multifunctional component Even though the radiator cap looks quite simple, its functions are essential. Its primary task is sealing the cooling cycle and preventing water from leaking out during driving. The warming up of an engine can cause pressure in the cooling system to rise to 1 – 1.5 bar. The radiator cap must be able to reliably withstand this pressure. The maximum pressure can generally be read on the radiator cap. If pressure gets higher, the radiator cap must be able to vent excess pressure from the cooling system. Otherwise, a hose or even the radiator itself could rupture. Therefore, a radiator cap is equipped with a valve at its bottom, recognisable by the pressure plate with its coil spring. This valve gently raises the cap for excess pressure to escape. This compromises the cooling system and it is only a safety measure in order to prevent greater damage. The radiator cap has an additional safety function. Under pressure it cannot be removed and it will lock after a 45˚ rotation. This is in order to prevent hot steam spraying in someone's face when removing the cap. The pressure escapes downwards and does not release the radiator cap until the system has sufficiently relaxed. Nevertheless, opening a cooling system under pressure is very dangerous. A burned hand is very disagreeable as well. Therefore rule number 1 when opening a radiator cap is: wait until the engine has sufficiently cooled down. In case of an overheated engine, this is at least 30 minutes. Reasons for excess pressure in the cooling system Excess pressure in the cooling system can develop in three ways. Cooling water level is too low: a low cooling water level causes the remaining water to boil. One litre of water generates 1650 litre steam. This explains why the pressure in the cooling system at falling water levels quickly rises. Overloaded engine: driving up the mountain fully loaded at full speed can bring even the most powerful engine to the limits of its capacities. Furthermore, too hot weather can cause radiator to boil. Defects of the pump, for example due to a loose driving belt of the water pump are also a typical cause. Defective cylinder head gasket: If the head gasket is burned through at the spot where engine pressure is guided into the cooling water, pressure quickly rises. Radiator cap defect A radiator cap permanently stands in contact with hot and cold water plus antifreeze agent and abrasion of rust from the cooling system. Initially this will clog the gasket. When oil gets in the cooling water due to a defective cylinder head gasket, disintegration of the gasket - as well as all other rubber parts of the cooling system, hoses included - is only a matter of time. The gasket can be replaced separately, though this makes little sense. The coil spring of the radiator cap valve suffers over time and loses tension. Therefore a radiator cap should be replaced if showing any defect. The life span varies a great deal. A radiator cap generally holds out for 10 years or longer. If the radiator needs replacement, it goes without saying that the radiator cap is replaced as well. This guarantees a defined new quality of this very important construction without any need for connecting the old with the new. If the car has an electronic radiator fan, replacement of the radiator requires replacement of the fan switch as well. The replacement of a radiator cap on the other hand, is very simple: wait until the car has sufficiently cooled down, turn the radiator cap 90˚ against the clock, remove and replace by a new part. New radiator caps are very cheap. They start at 5 – 6 euro (£4 – 5) in acceptable quality.