How a Coolant Reservoir Works

In order to understand the function of a coolant reservoir, it is necessary to first gain an understanding of how a cooling system works. You must have noticed that your car’s hood becomes hot after it has been running for some time. In addition, the radiator, set beside the car engine, also heats up and you should not touch it until the car cools down. This is because a vehicle’s running engine produces heat when the gas burns. This heat, if not countered appropriately, can cause the engine to overheat and thus damaging it. 

Connection to the Engine

For the purpose of providing a suitable outlet for the heat and keeping the engine cool, vehicles have a cooling system attached to the engine. This system consists of pipes or tubes that pass around the engine keeping it cool with the liquid that runs through them. A pump pulls the coolant or fluid up and pushes is through the pipes. The pipes run close to the cylinders in the engine block and keep a constant flow of cooling liquid circulating throughout. These pipes connect to a radiator that pulls out the heat from the liquid and directs it out of the vehicle.  

What is the Coolant Reservoir?

The coolant reservoir is a container that holds the excess or overflowing coolant, fluid or cooling agent which is used in the cooling system. It is usually a clear plastic bottle located near the radiator. You can easily find it by following the pipe of the radiator, which will be visible when you open the hood. The coolant reservoir is usually pressurized in the cooling system of newer vehicle models. It is attached to the radiator and the engine with “hoses” and is a central component in the system. The cap for the filler is also positioned on the coolant reservoir, making it necessary to pour the coolant into the reservoir instead of directly into the radiator.

Coolant to the Radiator

When the cooling system heats up, the coolant or fluid flows into the radiator. The radiator cap is like the air release system of a pressure cooker. When the radiator is hot, pressure builds up inside it and releases some of the coolant from the cap. This overflowing coolant passes into the coolant reservoir where it is stored until the engine cools.  

When the system cools down, the coolant stored in the reservoir is pulled back into the radiator by the reduced pressure. After this passing back of coolant into the radiator, the reservoir will normally be left with almost one third of the liquid coolant. Therefore, the coolant reservoir works as more than a bottle to hold excess fluid.

When Leaks Happen

Any kind of leak or break in the coolant reservoir will make the engine highly prone to overheating. Whenever the engine starts and heats up, causing coolant to run into the reservoir, more coolant will be lost. Additionally, the coolant dripping or leaking from the reservoir will cause the level in the reservoir to fall faster than usual, thus leaving your engine overheating more often and eventually damaging it.