Expansion tank cap (coolant reservoir cap) for your car

The coolant reservoir cap is an important component of the cooling cycle of a car. It opens the expansion tank, enabling the driver or mechanic to add coolant. A defect of the cap is rare, but occurs every now and then. The cooling cycle in a car The cooling cycle in a car serves to prevent the engine from overheating. Combustion engines function by burning fuel in small explosions and using the resulting pressure to generate kinetic energy. The engine has no use for the resulting exhaust heat which needs to be discharged. This is the task of the cooling system. Simple and small engines of lawn mowers or small motorcycles still manage by air cooling. The exhaust heat generated by the cylinders is lead away from the engine via cooling fins and dissipated by airstream or a blower. This once very popular way of engine cooling gradually became insufficient due to engines becoming more powerful. It was therefore replaced by water or liquid cooling. The liquid cooling is a cycle, constantly pumping cooling liquid through the engine. The cooling of the liquid, generally a mix of water and glycol, is provided by a radiator. In its turn the radiator is cooled by an airstream from the outside or generated by a connected blower. No system of water ducts is perpetually tight. A small loss of cooling liquid over time is therefore unavoidable. Especially in old cars, the coolant level should be regularly checked. The filling point for coolant is where you find the expansion tank cap. Expansion tank warning function In addition to its sealing function, the expansion tank cap has an important warning function for the driver. If pressure rises too strongly, the expansion tank cap opens the cooling system. This happens at a pressure of ca. 1.5 bar. Overheating occurs when:

- there is too little cooling liquid in the system - the engine is under excessive strain (e.g. driving uphill or overloading) - the cylinder head gasket is defective - the radiator is defective - the thermostat is defective

This will cause steam to escape from the coolant reservoir cap. In most cases, the engine control lamp will light up. The engine must be immediately switched off, as otherwise it will sustain heavy damage. Expansion reservoir cap defect Principally, the expansion tank cap is a durable component without any need for replacement during a car's life span. However, the expansion tank can develop fissures and then needs replacement. The expansion tank cap is then replaced as well. A defect of the expansion tank cap becomes apparent when it can no longer withstand the normal pressure of the cooling system. This might be a fault of the rubber gasket, which is situated at the bottom of the cap. In this case it makes sense to replace the entire cap. The constant switch from hot to cold can affect the cap's material integrity and replacing this cheap spare part is the best measure. The replacement of the expansion tank cap is as easy as it looks: the component can be simply removed for the general filling of the cooling system. Consequently it can be replaced by a new part. If a defect of an expansion tank cap is detected, it should be checked if this is the only occurring defect of the cooling system. This system ages evenly and therefore all components should be checked and if necessary preventively replaced. As the cap maintains pressure in the system, the quality of an expansion tank cap is very important. Even in branded quality, these spare parts are very cheap. There is no valid reason for choosing obscure cheap offers. A high-grade cap, e.g. by FEBI BILSTEIN, costs between 6 and 15 euro (£5 – £13).