Coolant expansion tank for your car

Coolant level always in check with the coolant reservoir

The coolant reservoir, a vessel also known as expansion tank or recovery tank, contains the engine's coolant. The tank indicates the current coolant level and enables checking the coolant's condition. The coolant tank is a sturdy component, though ageing can take its toll. Occasional replacement is recommended.

Coolant reservoir: function and position

The coolant tank is visibly situated in the upper area of the engine compartment, accessible and easy to fill. The expansion tank is a plastic vessel with a large, sealable opening at its top end and connections for the cooling circuit at its bottom. Level markers can be found on its side. Provided the expansion tank is intact, the driver can check the coolant level on the outside. Over time a coolant tank turns yellow, interfering with this function. At that moment, the tank is up for replacement. The coolant recovery tank has a safety system. A strongly overheated engine will cause steam to escape from the tank's cap, which is equipped with a pressure release valve, allowing a few seconds between overheating and total engine damage. Steam escaping from the coolant reservoir is the engine's last warning when the temperature gauge is non-operational or has been ignored for too long. The engine should now be switched off immediately.

Wear of the coolant reservoir

Coolant is more than just water, actually a mix of coolant, e.g. glycol and distilled water. The coolant's main task is preventing the water from freezing in winter. Glycol is important in all seasons, as it protects the engine against internal corrosion. Additionally, it lubricates moving parts such as the water pump or the thermostat. Chemical additives and temperature changes cause the tank's plastic to gradually turn yellow and become brittle. It is very important to use the prescribed coolant for the car at all times. Antifreeze is colour-coded. The wrong coolant can damage the gasket, hoses and ultimately the coolant tank, considerably shortening its life span. A defective cylinder head gasket affects the coolant tank as well, as oil is entering the cooling circuit, which has a corrosive effect on the rubber hoses and the plastic tank. If the tank is already damaged due to old age, it can burst. Should this happen, repair of the coolant reservoir is the least of your problems.

Replacing the coolant tank

The coolant tank is easy to replace. In most cases it is screwed onto the bodywork with one or two bolts. Disconnect the hoses and unscrew the bolts. Now it can be easily removed and replaced by a new component. There are several options for cleaning and clearing up a yellowed coolant reservoir. In case of any previous damage it cannot be repaired. Coolant reservoirs are really cheap and all the work is generally not worth while. When the coolant reservoir has been soiled by oil mixing with the coolant, the coolant hoses and possibly the radiator should be replaced. Oil is a corrosive agent for rubber hoses which must be completely removed from the cooling circuit. If there is no other option, all detachable components must be replaced – of course only after repair of the cylinder head gasket.

Coolant tank reservoir: costs

Costs for a new coolant reservoir depend for a great deal on the car brand, type and the quality of the spare part. The choice is extensive and for older cars cheaper coolant tanks can be used as a temporary solution. Nevertheless, only branded products guarantee a durable use. Prices for a new coolant reservoir start at ca. 15 EUR (± £13). If the tank has a temperature sensor, it makes sense to replace this along with the tank. This applies to the tank cap as well, as in most cases it contains the pressure release valve.