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Can You Put Water in the Coolant Tank? Find Out Here

Avatar Adie Tinkle -

Can you put water in the coolant tank or not? Knowing the answer to this question can help you follow a better approach when your vehicle needs coolant. 

Your cooling system needs coolant or antifreeze in order to regulate the engine’s temperature. Therefore, regularly checking your vehicle’s coolant level is important, especially if you are about to leave for a long trip. However, if your vehicle runs out of coolant midway to your destination and reaching a shop to buy more coolant is not possible, can you put water in your coolant tank? Let’s find out.

Can You Put Water in the Coolant Tank?

Coolant and water are added in an equal ratio of 50:50 for them to work and maintain the engine’s temperature. This mixture hampers the freezing or boiling of the coolant under severe weather conditions. However, if water was enough for the vehicle’s engine, there was no need to manufacture coolant or antifreeze. 

Even though you can add water to the coolant tank, it should be only done in case of emergencies. If your engine is overheating and you do not have coolant available, you can add water and let the engine cool down. However, make sure to resolve the issue by adding coolant mix as soon as you can. 

This is because the water boils and evaporates in hot temperatures while the coolant stays in the liquid state no matter how high the temperature range goes. Moreover, water freezes at much higher temperatures and causes corrosion and electrolysis. 

Reasons for Sticking with a Coolant 

As you now know, water is not an ideal fluid when it comes to replacing it with coolant. There are some benefits that only coolant can provide, and these include 

High Boiling Point 

Unlike tap water, the antifreeze solution has a higher boiling temperature. This higher temperature gives the engine more freedom to operate without needing to boil the coolant inside the pipes. 

Low Freezing Point 

Mixing water and coolant together decreases the overall freezing temperature to even lower. It gets to about -35 degrees Fahrenheit. It means that even if the outside is freezing, the coolant inside your tank will stay in the liquid form and will keep doing its job. 

Protection Against Corrosion 

Adding water alone to the coolant tank can be harmful to the metal parts. However, when you add an equal ratio of water and antifreeze, the water does not easily bond with the metal ions. The rusting issue can be very expensive and hectic to deal with. 

Why should I not put 100% coolant in my car?

The coolant works better than water to keep the engine cool. However, adding only coolant is not a good idea as it will turn to jelly at about -10 degrees Fahrenheit. Therefore, it is best to add coolant and water in a 50:50 ratio. 

Can water cause corrosion and electrolysis in the water tank?

Tap water contains minerals that can leave deposits in the radiator, which can affect the cooling system’s performance. Moreover, it can also be corrosive, especially in high temperatures. Corrosion and rust can cause malfunctioning in the cooling system. The majority of the coolant and antifreeze mixes contain propylene glycol and ethylene glycol that will not cause corrosion on metals that easily, and they also contain additives to prevent corrosion. 

I have accidentally put water in my coolant tank. What should I do?

If you have accidentally added water to the coolant tank, what should be your next step? The first thing to do is flush the coolant system entirely. Let your vehicle rest for a while, as water can run across pipes in warm temperatures, which can burn you. So, waiting a while and letting everything cool down is better. 

Then, open the coolant tank’s cap and flush out everything. A mistake that the majority of people make is adding coolant directly when there is still water present. Though it might not seem like a big deal, the water is not in its ideal condition. Because of that, the coolant will not work as efficiently as you might expect. It’s best to mix the coolant with a new batch of distilled water, and your vehicle will go back to normal without any disturbance. 

Should I add cold water or room-temperature water to the coolant tank?

In case of emergencies, prevent yourself from adding cold water as a replacement for the coolant mixture. This is because cold water can cause damage to the shape of engine walls as engine walls get hot from operating. It is preferable to use water at room temperature. 

Is distilled water a better choice than tap water for a coolant tank?

Adding distilled water is a better practice than adding tap water in the coolant tank. This is because tap water contains a lot of unfiltered minerals, such as copper. The copper can stick to the wall of the engine and create rigid layers. Distilled water is free from various elements and minerals, so using it is a better option.

What coolant ratio is best in the hot weather?

if you live in a place where the temperature never goes below 26 Fahrenheit,  your vehicle will perform at its peak with a 90/10 ratio all year long. However, if the weather can drop to about -10 Fahrenheit and can go up to 95 Fahrenheit in summer, it’s preferable to use a 60/40 ratio. 


You cannot alternate water with antifreeze in your vehicle. Adding water instead of coolant in your coolant tank can cause damage to your vehicle. Though you can add water to the coolant tank if it’s an emergency, it is important to be careful about this and keep a separate bottle filled with coolant and other spare accessories with you.

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