Can we use plain water instead of coolant when the car radiator runs dry? Will that cause damage to the engine?

 Can we use plain water instead of coolant when the car radiator runs dry? Will that cause damage to the engine?  

It wouldn't be a good idea to leave your car radiator run dry to the point that the engine is overheated and causes severe damages. However, what if it's an emergency and we don't have coolant to fill in time? Is it okay to use plain water instead? Will that affect the radiator or parts in the cooling system or the engine of our car in any way? Let’s find out the answer!

First of all, let's understand more about radiators and coolant. Radiator in  a car is a device that exchanges heat between coolant and outside air in order to lower the coolant temperature to the suitable level before flowing back to cool down the engine and other parts again. It prevents the engine from abnormally high heat or overheating that can lead to severe damages.

The coolant carries the heat away from the metal surface of the engine parts where the liquid flows by. This helps maintain the temperature of the combustion chamber, engine parts and engine oil in the proper level for continuous operation at maximum efficiency. The coolant also contains rust and corrosion inhibitors to protect the radiator, parts in the cooling system and engine parts for a longer service life. Most coolant is colored with fluorescent color that allows us to easily detect the leaks around various parts in the cooling system.

What if the coolant in the reservoir and radiator dries out? Can we add plain water instead?

The answer is “Yes, you could, BUT only temporarily or in an emergency. Long-term use is not recommended and you should immediately add new coolant when it is available.” As water does not contain inhibitors that help prevent corrosion and rust in the cooling system, filling it would increase the risk of leakage of the radiator, wear and damage of the water pump. Doing so can also lead to corrosion of the metal parts of the engine that will allow water from outside to leak into the engine oil. In addition, because water has a lower boiling point than glycol based coolants, it increases the risk of vaporization and foaming in the cooling system, which can be harmful to the engine as well.

Therefore, it is highly recommended to use coolant to fill your car's radiator as the coolant contains a mixture of glycol (Ethylene Glycol or Propylene Glycol), making the coolant boil at a higher point and freeze at a lower point when compared to water. This difference will help prevent water from boiling better, especially when the engine has to work continuously with high load resulting in heat accumulation in the engine. It can also help prevent water from freezing. In addition, the coolant has the inhibitors that protect the radiator, parts in the cooling system and engine parts from rust and corrosion as well.

To save yourself the trouble, it is recommended that you take care and check that the coolant level in the coolant reservoir is always at the proper level (between Min and Max levels). Also, make sure that you have the coolant changed at specified intervals, e.g. every 100,000 km or 5 years, whichever comes first. However, the entire cooling system should be changed immediately when sludge is observed in the radiator or the coolant is highly dirty/contaminated so that the cooling process of our car’s engine can work effectively for a long time.

ONCE AGAIN! It is not recommended to use plain water to fill the radiator because, in addition to having properties that are inferior to coolant, it can also negatively affect your cooling system and engine parts in the long run.

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