What Happens When Coolant Mixed With Water

Coolant and water are two liquids that you don’t typically think of mixing. For example, when your car overheats, the mechanic will usually recommend adding more coolant to the system instead of water.

However, if it comes down to choosing one or the other in an emergency situation, which liquid is better for your car?

Fortunately, both liquids are safe for your car. In fact, they can even be used together with a little bit of engineering. When coolant mixed with water, there are several side effects.

But with a little bit of background knowledge and precautionary measures, neither mixture is dangerous for your engine or you as a driver. Let’s take a look at what happens when you mix these two liquids together.

What is Coolant?

coolant and water
Image Credit: grimmermotors.co.nz

Coolant is a liquid that is used to regulate the temperature inside a car’s engine. It is a mixture of ethylene glycol, water, and other additives that keep the engine from overheating.

If your engine overheats, then it can cause serious damage to the engine as well as lead to a dangerous situation on the road. 

Coolants are designed to transfer heat away from the engine and into the radiator, where it is cooled by the air passing through the radiator. The radiator is designed with cooling fins to increase the surface area that the air comes into contact with, which in turn increases the rate of heat exchange between the air and the coolant. 

Coolants can be made using different chemical compositions that can affect their boiling point, freeze point, corrosion resistance, and toxicity. The most common coolants for automotive use are ethylene glycol-based. 

Ethylene glycol-based coolants are not water-soluble, so if the coolant leaks out of the engine, it will not cause a corrosion problem in the surrounding areas.

Ethylene glycol-based coolants are also non-toxic to humans but can be harmful to aquatic organisms.

Mixing Equal Parts Water and Coolant

If you are short on coolant, then you can try mixing equal parts water and coolant. However, if you add too much water to the coolant, then it might cause the coolant to boil and leak out of the engine.

Another potential problem is that if you add a large amount of water to a small amount of coolant, then the water may not be able to absorb all of the heat in the system. 

Adding water to the coolant can also dilute the corrosion inhibitor in the coolant, decreasing the life of the engine components. If you have no other choice but to mix water with your coolant, make sure to frequently check for leaks, especially around the engine.

Coolant Mixed With Water: Pros and Cons

When you try to mix water and coolant, you’ll notice the coolant turns from a blue color to a milky white and that’s not a good thing. If you see this in your coolant, then you know that the water and coolant have blended together.

When you mix water and coolant together, the coolant loses its ability to regulate the temperature in the engine. 

The coolant no longer works as intended, and it will not be as effective in protecting the engine. Coolant is designed to be more viscous at low temperatures and less viscous at high temperatures. When the coolant is cooler, it is more viscous and is pushed out by the engine. 

When it is hotter, it is less viscous and is pulled in by the engine. This cycle allows the engine to always have the protection it needs. Now, when you add water to the coolant, the coolant remains more viscous at all temperatures.

This change in the chemical makeup of the coolant causes it to no longer work as intended. The engine may also be harmed as a result of the now reduced protection.


1. It can help to keep the engine coolant system from freezing in extremely cold weather. 

2. It can help to keep the engine from overheating in hot weather. 

3. It can help to protect the engine from corrosion. 

4. It can help to keep the engine coolant system clean. 


1. It can cause the engine coolant system to become clogged. 

2. It can cause the engine to overheat. 

3. It can cause the engine to corrode.

Disadvantages of Mixing Equal Parts Water and Coolant

In addition to the issues that the engine faces when mixing water and coolant, you will also be putting yourself in danger. When you mix water and coolant, you increase the risk of corrosion occurring in the engine. This can cause serious problems, as well as a decrease in the life of the engine. 

When corrosion occurs inside the engine, it can lead to serious problems, such as clogs in the cooling system that can cause overheating and engine damage.

If corrosion occurs in the fuel system, it could cause a fuel leak and the risk of fire. If the corrosion is severe, the engine may need to be replaced.

Disadvantages of Mixing Only Water

If you only have water and no coolant, then you need to find a way to get more coolant into your car. If your car’s engine overheats, then the engine can become so badly damaged that it has to be replaced.

If you don’t get coolant into your engine, then the engine can overheat to the point where it seizes up and stops working. 

Overheating can also cause serious damage to engine parts, such as pistons and cylinder heads. When the engine overheats, the coolant inside the engine heats up and turns to steam.

If the coolant can’t get back down to its normal temperature, then it will turn into steam inside the car and collect in the radiator. 

At that point, the car’s engine will stop working, as it will no longer have a way to transfer heat away from the pistons and other engine parts.

Summing up

Mixing equal parts water and coolant can be very dangerous. Even if it works temporarily, the damage done to the engine is irreversible. This mixture can also cause corrosion in the coolant, which can lead to serious damage in the long run.

If you only have water, then you’re better off using it than letting the engine overheat. But it would still be better to find some way to get coolant into the engine.

If you are in an emergency situation and need to put water in your car’s engine, then make sure it is not from a contaminated source. 

If it is, then the water can contain harmful minerals and bacteria that can damage the engine and put you at risk for infections. If you have to mix coolant and water, make sure to use the right proportions.

If you add too much water to the coolant, then it can cause corrosion in the engine. And if you add too little, then the engine can overheat.

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