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How Long to Let Engine Cool Before Adding Coolant

February 23, 2024 | Victor Lukasso

Coolants help regulate the engine temperature preventing it from overheating or damage. However, you must know how long to let the engine cool before adding coolant.

Knowing this often comes in handy when your vehicle goes off or starts overheating on the highway due to low coolant levels, as you’ll save yourself from panicking and do the right thing.

While it’s possible to add coolant when the engine is hot, Autobasics advises letting the engine cool down for at least 30 minutes or one hour before adding coolant to ensure the process is done safely and effectively.

This will give the engine enough time to cool off, prevent leakage in the radiator pipes and cracks in the engine block, and prevent the coolant from boiling, which could cause burns.


This article discusses how long you should let an engine cool before adding coolant and why it’s essential.

How long to Let the Engine Cool Before Adding Coolant?

Auto experts have confirmed that it takes your engine 30 minutes to get to room temperature, and it’s safe to add coolant to it at this point. However, depending on how long the engine has been operating and the size or type of engine, you can wait an extra hour or two.

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With the above point, it’s safe to say that the duration required for an engine to cool down depends on several factors, such as the type of engine, the size of the engine, and the operating temperature of the engine, but 30 minutes is enough to drop the temperature to a room temperature.

For instance, an engine that has been in use for over 10 hours would require more time to cool than one that has just been used for 30 minutes.

Also, engines made with iron or cheap aluminum will heat up faster than those made with Aluminum, Magnesium, or ceramic matrix composite.

In addition, Before adding coolant, it’s essential to check the owner’s manual to determine the type, amount, and level of coolant recommended for the specific engine. Different engines require different types of coolant, and it’s essential to use the correct type to ensure proper engine performance and prevent damage.

Also, endeavor to add coolant to the overflow tank to ensure the engine cooling system doesn’t go empty. The overflow tank is located near the radiator and stores excess coolant.

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Do I have to let my car cool down before adding coolant?

Most people might doubt the motion of letting your car Engine cool down before adding coolant, but it’s necessary if you want the process to be safe and effective.

And Yes, you must let your car cool down for at least 30 minutes before adding coolant or antifreeze.

Here are the reasons why:

Incorrect coolant reading

If you pour coolant into the engine while still hot, you’ll get an incorrect reading when you measure it with a dipstick. This occurs because the coolant hasn’t settled, leading to improper readings.

Additionally, if the engine is not cool enough, the coolant may not circulate properly, leading to an overheating problem and potentially causing damage to the engine.

Burns or Injuries

If you add coolant to a hot engine, the coolant may vaporize or boil over, flow out of the tank, and even get in contact with your skin, which can result in burns when it gets in touch with your skin.

So, I’ll advise you to let the engine cool down before you open the radiator cap to add coolant or antifreeze.

Cracks in the Engine Block

The block might crack due to expansion if you add coolant to a hot engine. A typical example is when you add a cooling substance to a hot metal, it will shrink and deform.

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Radiator Pipe Leaks

The common cause of radiator pipe leaks thermal expansion. When you introduce coolants through a hot radiator pipe, it’ll lead to cracks in the wall of the pipes.

This implies you’ll need to replace the radiator pipes before your car can function correctly.

Engine Damage

If the engine is too hot, the coolant can boil over, causing damage to the engine.

That’s it.


Is it okay to add coolant when the engine is hot?

Adding coolant when your engine is hot is never advisable to prevent burns, cracks, or total engine damage. You should wait at least 30 minutes for the engine to cool off.

How long should I let my car cool down before adding coolant?

Under normal driving conditions, waiting 30 minutes is okay before adding coolant to the radiator.

How long should I wait to add coolant to a hot engine?

If the engine is scorching, it may take longer to cool down. It’s best to let the engine cool down for an hour or more before adding coolant.

Can I drive immediately after adding coolant?

Once you are sure your coolant is gauged correctly, you can drive off immediately after adding coolant.

What will happen if the coolant is low?

If the coolant in your car is low, you will experience overheating or frequent engine seizures. If you continue driving with these symptoms, it could result in permanent engine damage.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.