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Can You Use Water Instead of Coolant (In A Pinch)?

Can You Use Water Instead of Coolant (In A Pinch)?

How can you keep the engine cool if you’re out of coolant? You might’ve seen someone use water in a movie before. 

Can you actually use water to replace your coolant in a pinch, though?

Water can be used in place of coolant in an emergency. However, doing so still poses a risk as water does not have the same properties and could result in the engine overheating.

It may help reduce the engine’s temperature a little bit, but it’s risky. 

Water doesn’t have the same properties that you’d find in actual coolant

Coolant does more than just keep your engine cool. It also protects it against corrosion, and water doesn’t!

What Happens If You Use Water Instead of Coolant?

Technically, nothing happens if you use water instead of coolant, at least not right away. Water can keep the engine from overheating if you don’t have anything else. 

However, you shouldn’t rely on it to protect the engine all the time. 

Coolant has special properties that make it great at what it does. 

One of them is its boiling point. Water boils at 212°F. You can mix it with 50% glycol antifreeze to raise the boiling point a few degrees. 

However, the coolant has a boiling point of 375°F if it doesn’t have any water in it. 

That’s pretty close to the operating temperature of your engine, so it won’t evaporate. 

Part of the reason water isn’t great for this is that it evaporates too fast

It has a relatively low boiling point when you compare it to antifreeze. You’ll start boiling it within a few minutes of driving, making it disappear. 

Driving with water for too long would overheat your engine since it’ll all evaporate. That’s why you should only use water if you’ve got to travel a short distance and don’t have any coolant. 

Another reason water isn’t great is that it freezes pretty easily. Water starts to freeze once it’s at 32°F. 

Dropping lower than that would cause it to freeze inside the engine, cracking the block. 

Letting water freeze in the radiator could actually destroy your whole coolant system. Antifreeze is going to prevent that from happening, even when it’s below freezing

Water also contains a ton of minerals and other contaminants. These deposit along the inside of your engine when you’ve got water in the radiator. 

Plus, water may cause your engine’s metal to start rusting

Using antifreeze helps protect the engine from corrosion since it doesn’t deposit anything.

It won’t cause rust to start forming inside of it, either. Some of them even have additives that prevent rust formation altogether. 

Risks of Using Water

What’s going to happen if you put water in your car’s radiator and drive for a while? 

Well, the first thing that’s going to happen is it’ll start boiling. 

Boiling water evaporates away from the radiator, leaving it empty. After it’s all gone, your radiator won’t cool the engine anymore. 

That’s when you’ll notice it’s overheating, sending temperatures soaring. 

You can pull over to let the engine cool down, but you’ll have to add more water to its radiator. 

Driving too much could destroy the entire engine if it’s overheating. 

The other thing you’ll notice is how the engine acts once it’s near freezing outside. Any water you put in the radiator would start freezing at that temperature, making it expand. 

Letting the water freeze while it’s in the radiator could break your coolant system. 

Finally, putting water in the radiator causes the engine to corrode faster than usual. That’s because water promotes rust formation, and it carries contaminants. 

Anything in the water gets deposited in the engine’s interior. 

After enough time, these deposits could stop the radiator from working at all. 

What to Do If You Do Use Water

Not everyone knows when they’ll need to top off their radiator with coolant. So, they may not have any on them when the time comes. 

How do you use water without destroying the engine if you’re out of coolant? 

Using water should be a last resort, first of all. But, if you’re going to use it, you can follow this advice. 

Try mixing it with the remaining antifreeze in your radiator. 

A 50/50 mixture is going to have better properties than 100% water. So, it wouldn’t damage your engine as much if you had some in the radiator. 

Pour a little water into it without draining whatever is in there already. 

After putting water in the radiator, you should buy antifreeze as soon as possible. 

You don’t want to drive with water in there for long. Otherwise, you could destroy the engine block, bricking the car. 

Go to a nearby store where you’ll be able to buy some antifreeze. Then, pick some up that’s the right kind for your car. 

You’ll have to drain the water that’s in the radiator before putting antifreeze in there. 

Usually, you can drain the radiator by opening a plug on the bottom, letting everything seep out. Put the antifreeze in there once you’ve finished removing all the water. 

It’s not easy to get all the water out after you’ve filled up the radiator with it. So, you may need to try this a few times to get everything out. 

You can drive once you’ve got the antifreeze in your radiator. 

We’d suggest topping off the antifreeze after you’ve driven a little bit. Most of the remaining water should evaporate while you’re driving. 

That’s when you can finish putting the antifreeze in your radiator. 

What Is Coolant and How Does It Work

Antifreeze and coolant are often confused with one another. They’re very similar, but there are a couple of differences. 

Most antifreeze is either ethylene glycol or propylene glycol. 

These don’t freeze at the same temperature as water, so it remains liquid in the cold. There are several types of antifreeze available, labeled by color.

You’ve got to use the right color to fill up your radiator if you don’t want to damage it. 

Coolant works by absorbing heat from the engine whenever it’s turned on. 

It gets sent through a network of tubes, interspersed throughout the engine bay. Heat leaves the engine and enters the coolant as it passes through. 

Heated coolant makes it to the radiator after leaving the engine. That’s where it transfers heat to the ambient environment. 

Most radiators have a fan that blows on the coolant lines to speed up this process. 

Your coolant also prevents the engine from freezing when it’s too cold. That’s because it’s made using chemicals with incredibly low freezing points.

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Zach Reed

Hi, I'm the founder of! Having owned a wide variety of vehicles in my life, I was astounded at how hard it can be to find answers to common automotive questions. Rather than sit idly, I decided to create this website to help others!