Can you use water instead of coolant for the engine?

This is a question that is commonly asked in the automotive field. The reasons of using only coolant or water or both for the car’s engine will be explained in this article

The quick answer is yes, you can use water instead of coolant for the engine, but only as a temporary solution, for example, a pipe broke on the road and the coolant leaked and you don’t have any spare, water can be added and preferably distilled. Regular tap water is also fine too

When you arrive, be sure to change the water with coolant by flushing the cooling system. Also, this emergency suits well only in the warm season, when temperatures are above the freezing point. Also if it’s too hot outside, the water can boil away.

Mixing water with coolant is a normal process only when the coolant is not diluted, and only distilled water is allowed. You can read here about the coolant types.

You should not mix ethylene glycol antifreeze with water and use it in the long run, because when its initial chemical composition changes, it loses most of its properties, like optimal viscosity, heat transfer, detergent properties, corrosion protection. And because of this, the foaming process is activated. It is not so easy to wash the cooling system from the foam later.

Why use coolant instead of water for the car’s engine?

It is recommended to use coolant all the time because it helps to ensure that the engine warms up evenly and prevents it from overheating. Antifreeze can withstand high temperatures up to 110 ° C (230 °F), while not evaporating as water does, it does not freeze at low temperatures, due to its composition. But since the antifreeze contains water, isn’t it easier to use only it in the cooling system? Not really.

Unlike coolant, water has the following cooling disadvantages for the engine:

  • Can cause metal corrosion. Over time, the engine will simply begin to rust from the inside;
  • Does not have washing properties, which accelerates the wear of the circulating pump. The exception is systems with closed bearings that do not come into contact with the coolant;
  • Has a lower boiling point.

Why is the use of water dangerous for the engine?

Experts do not recommend resorting to this measure. There are several reasons why. First, water is often hard, and this affects the engine. Secondly, hard water can clog the radiator, which will cause the engine to constantly overheat. Third, at freezing temperatures, water freezes and can simply break the parts of the cooling system.

In theory, water is no less efficient in terms of heat transfer than coolant. If water is poured into the cooling system, then the engine will still work normally and cool. Maybe the final temperature will be only 2 – 3 degrees higher, but there will be no significant difference.

Only distilled water is recommended. In other types of water, for example, drinking water, there is too much admixture of salts and limestone. 

These substances practically do not harm the metal, but at the same time it can lead to a clogged radiator, which will deteriorate the cooling efficiency, and over time, microcracks will form on the radiator.

Also, quite often, air jams can form in the cooling system, since in water, in contrast to coolant, a much larger volume of oxygen is “dissolved”. In the presence of an airlock, the normal process of coolant circulation is also disrupted, the pump simply stops pumping water (which also overheats).

Water has a higher rate of change in volume when the temperature is changing. Because of this, when refilling to the maximum, after warming up the engine, steam will begin to get put from the reservoir. And if the valve is also faulty, then the coolant reservoir can be completely damaged.

If the air temperature reaches the freezing level, then the water will freeze. This leads to damage to the elements of the cooling system, like pipes and radiators will burst, and damage to the engine block.

When water can be added instead of coolant?

It is possible to use water instead of coolant only in an emergency, and there is no coolant at hand. It is worth considering that water will not be as effective as antifreeze. The engine operating temperature often exceeds 100 ° C (212 °F), this will cause the water to boil away, and its vapors will only accelerate engine overheating. If you have to travel longer distances, check the coolant reservoir often.

How to return the cooling system to normal after filling it with water?

To minimize the negative effects of using water instead of coolant, you should use distilled water instead of tap water. It is free of salt and does not form scale. But even after using distilled water, it is necessary to return the system to its normal state.

This is very simple to do, you need to rinse it. This is done as follows:

Warm the engine slightly, and then let it cool down a little. Only after that, you can drain the old fluid. 

Add cleaning agent into the cooling system, which can be purchased at any car store. Each of them has its own nuances in use, which are indicated in the instructions, they should not be neglected. After flushing, you can add coolant into the system.


There is only one conclusion, you can use water only in exceptional cases , at other times you need to use antifreeze to avoid damage to the cooling system.

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