Can You Use Water As Coolant? Here’s The Answer

Many car enthusiasts and everyday vehicle owners hold the common idea that distilled water and anti-freeze are pretty much interchangeable in the engine of a car. This assumption is particularly common if you live in a warm climate where chances are you won’t ever be driving at temperatures below 32 F.

It’s uncertain when or exactly from where this idea may have originated. Perhaps it was born from the desire to find a cheaper alternative to cool the engine, or maybe somewhere along the line it just seemed to make sense that the two substances would create the same outcome.

Whatever the reason, the topic still confuses many motorists and the core question still remains; can you use water instead of coolant in your car? If you considering making this seemingly simple substitution, continue reading to find out why doing so many ends up ultimately being a costly mistake.

What is Coolant (also known as Anti-Freeze)?

Coolant or anti-freeze (the words are interchangeable) is a liquid solvent made up of ethylene glycol or propylene glycol mixed with water. The resulting solution both lowers the freezing point (to -35 F) and raises the boiling point (to 223 F) of a liquid.

The ethylene glycol mixture is the one that you will find used in automobile applications (and the one discussed in this article) and the propylene glycol mixture is used primarily in places where accidental ingestion might occur, such as food-processing systems.

The coolant used in automobile applications also has “corrosion inhibitors” added to it to help protect the vehicle engine’s components (often made of copper, aluminum, brass, cast iron, or other metals) from corrosion. Nobody wants to end up with an engine that has rusted, as it will certainly lead to costly repairs.

How Does Coolant Work?

As you drive your car down the road each day, you don’t think about it, but the engine components getting you where you need to go generate a lot of heat. If these parts are not continuously cooled, it will result in significant engine damage or even a complete engine failure.

The way coolant works inside of the engine are fairly simple and straightforward. Initially, the coolant is poured into a separate compartment connected to the radiator (the overflow tank). From there it travels throughout the engine in a circular loop to effectively remove the generated heat.

The steps involved in this cycle are as follows:

  1. The coolant travels out of the reservoir and into the water pump.
  2. From there it enters the engine and removes the combustion-generated heat from the cylinder heads and valves.
  3. It continues through the heater core (the unit that supplies heat to the passenger section of the vehicle) and provides heat for the passengers in the vehicle absorbing heat there as well.
  4. Finally, the heated coolant returns back to the radiator where it is cooled down in preparation for repeating the cycle. A fan that blows directly on the radiator assists with this cooling-down process.

This flow of coolant happens the entire time that the engine is running and the coolant constantly recirculates throughout the engine to absorb more heat.

The Importance of Coolant

As you can probably guess by now, coolant is an extremely important part of your car’s engine system, as it helps to keep your car engine running efficiently. A smoothly running engine will require less maintenance and eliminate costly repairs on your vehicle.

Many people mistakenly think that if they reside in a warmer climate, coolant isn’t as important and could be substituted with water because their engine is not susceptible to freezing temperatures. However, this assumption is simply wrong.

To illustrate the importance of using engine coolant, look at the following examples which describe what would happen if you used water instead of coolant in both warm and cold climates.

Warm Temperature Climates

A young woman opens the car hood under the sun.

In warm climates, the heat created by regular internal engine combustion can build up extremely quickly. This extreme temperature can cause issues with the cylinder head or head gasket and many other parts of the engine.

If one were to use water instead of coolant, this catastrophic engine damage would occur quite quickly as we all know that when water reaches an extreme temperature, it will boil. If the water in your engine reaches a boiling point, it will soon do what boiling water in a pan does and evaporate leaving you without any liquid left to cool your engine at all.

Cold Temperature Climates

A car covered with snow.

The opposite occurs if you use water instead of coolant in cold temperature climates. If the water in your engine gets too cold, it will freeze inside of the engine. Frozen water in the engine will not be able to flow freely throughout the components and lead to cracks in the radiator, heater core, engine block, and other extensive damage to the components of your car’s engine.

As mentioned earlier, because of the way coolant is designed, it can effectively run through your vehicle’s engine regardless of the outside temperature without boiling or freezing. Coolant will always stay in a liquid state regardless of external temperature factors.

On the contrary, water will always react the same way to hot or cold temperatures – it will always boil or freeze. Additionally, plain water lacks the anti-corrosion components that are included in coolant and over time would certainly rust or corrode the metal parts of the engine.

As you can see from these examples, coolant is most definitely a necessity for keeping your engine well-maintained and running. Keep in mind though, that not all coolant is completely the same, as the metals used in engine systems differ by manufacturer.

Therefore, it is always best to use the coolant product recommended by your vehicle’s manufacturer, as they have each created a coolant that will work best with their specific system.

How to Fill Up Your Car’s Radiator

Since coolant is such a vital part of keeping your vehicle up and running, you should make sure that you check it periodically to ensure that your vehicle is maintaining an adequate radiator fluid level.

A mechanic is checking the radiator antifreeze of a car engine.

Many times this service is also performed when you take your vehicle for an oil change or other regularly scheduled maintenance, but learning how to properly check and fill your car’s coolant can help you to maintain peace of mind that your engine is efficiently functioning in between those other regularly scheduled checks.

It is important to note that most modern vehicles have a sealed cooling system and do not require any “topping off” of the coolant. However, you still should not neglect regularly checking the coolant level to ensure it is adequately maintained.

To Get Started You Will Need:

  • Gloves
  • Towel or a Rag
⚠️ IMPORTANT NOTE: Heat has somehow built up inside of the radiator. Serious injuries can and have occurred from opening the cap on a radiator that has built up too much heat inside of it.

Steps to Check and Fill Your Radiator

1. Verify that you have cooled your engine. Park and turn off the car and let it sit long enough that the radiator is cool to the touch. You can feel the hood of the car to confirm if it has cooled. If the hood of the car is cool, it will indicate that the engine has cooled. If you have been recently running the car, it may take as long as 30 minutes for the engine to cool down.

2. Open the hood of your vehicle. Locate the “hood-release” lever inside of your car and pull it to disengage the hood. Then, reach under the front of the hood and pull it up completely. If your hood is not designed to stay in place on its own, there should be a metal rod underneath the hood that will prop it up and keep it open.

3.   Locate the radiator cap and open it. Most newer cars have radiator caps clearly labeled. If your cap is not labeled, refer to the vehicle’s owner manual to locate it. Use a towel or rag to loosen the cap and lift it off the radiator. Remember, DO NOT open the radiator cap if it is hot as it could lead to very severe burns.

Mechanic man opening a radiator cap.

4.   Check the fluid level in the radiator. The radiator overflow tank is usually see-through, so you should simply be able to look at the tank’s fill level markings to determine if the coolant level is too low.

If the coolant level is low, you will need to add more coolant by following the additional steps outlined below. If the coolant level is sufficient, you can replace the radiator cap at this time.

Materials Needed to Add More Coolant

Steps to Add More Coolant

1.   Locate the expansion tank. This tank is a small reservoir on the side of the radiator that collects any fluid that spills out when the radiator overflows. You should add coolant to this tank rather than directly to the radiator, but ensure that you do not fill it up all the way. The coolant expands as it heats up, so it will need the proper room to expand.

💡 NOTE: If your coolant level is low, but your overflow tank is full, you should have a mechanic inspect the system as it could indicate a problem with the radiator cap and overflow system.

2.    Mix the coolant with distilled water. Mix the coolant with distilled water in a 50/50 ratio by filling an empty radiator fluid bottle halfway with water and then topping it off with coolant. You can use until a 70% coolant to water ratio, but a 50/50 ratio tends to be the most efficient. It is very important that you use only distilled water when creating this mixture.

3.   Pour the coolant mixture into the overflow tank. Remember to not fill the overflow tank the entire way to allow for expansion. If your vehicle does not have an overflow tank, you can pour the liquid directly into the radiator, ensuring that it does not go over the fill line.

4.   Replace the radiator cap. Make sure you securely and properly replace this component. Refer to the owner’s manual instructions, if necessary.

5.    Start the vehicle’s engine. As you start the engine, listen for any unusual sounds and check that the temperature fan and cooling sensor are in working order. Any clanging or humming noises indicate that the cooling fan may not be operating properly and should be further checked.

6.   Look for any leaks. Inspect the radiator hoses to verify that there are not any holes. If you seem to be quickly losing coolant, even after replenishing it, you may have an internal leak, which would require a mechanic’s attention.

7. Reserve any remaining coolant in its proper container. Be sure to tightly close the container and store it in a location not easily accessible by children or animals. If you need to dispose of any unused or old coolant, refer to and follow the procedures and regulations outlined by your particular state to ensure safety compliance.

So, Can You Use Water Instead of Coolant in Your Car?

Now that you know the basics of why a proper coolant is critically important to the efficiency and protection of your vehicle’s engine, there should be no question in your mind that water is simply NOT a suitable replacement for coolant inside of a car.

The risks involved in taking this shortcut are simply too many to take. Coolant and water DO NOT operate the same way within a vehicle’s engine and by not utilizing a coolant specified by your vehicle’s manufacturer, you are setting yourself up for a poorly running vehicle and ultimately costly engine repairs.

Man filling water to a car radiator.

Only in an absolute emergency, should you even consider using water to cool your vehicle’s engine and if this type of emergency occurs, you should make sure to absolutely replace the water in the radiator with the proper coolant as soon as possible.


We hope you have enjoyed learning about this often overlooked part of the car’s engine, which is ultimately the “heart” of your vehicle. Remember, preventative maintenance of your coolant levels and using only a proper type of coolant is much less expensive than repairing an overheated engine.

Have you ever used water instead of coolant in your vehicle? Or do you have any other unanswered questions about coolant? If so, please drop us a comment below. We’d love to hear your thoughts.

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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