Does The Car Need To Be Running When Adding Coolant?

Switch off the engine whenever you want to add coolant. Running the engine and adding coolant could damage the engine and also scorch your skin.

If you add new coolant, you need to switch off the engine and wait for it to cool. It is safer this way for both you and the engine.

Also, you must know what to do after putting coolant in vehicle. It will help the coolant last longer and protect the engine from any potential damages from changing or adding coolant.

what to do when adding coolant

How to put coolant in your car safely

Adding coolant to a vehicle is straightforward. However, there is a procedure that needs to be followed. You need a proper guide that shows you what to do when adding coolant.

Below is a well-detailed and easy-to-follow step to safely add coolant to a car.

Step 1: Get all the necessary tools and supplies to add the coolant.

  • New coolant: You must note that there are different types of coolants being sold. Buy a coolant product recommended by your vehicle manufacturer.
  • Gloves: Coolants are made of toxic chemicals, and when in contact with your skin, they could cause skin irritation. Wearing a glove will prevent any damage to your skin.
  • Funnel: A funnel will help avoid wasting the coolant well pouring into the radiator or reservoir.
  • Vehicle manual: The vehicle manual will help locate important parts like the coolant reservoir, radiator, and drain plug.
  • Rag: A rag is needed to help clean any mess that must have happened when adding the coolant.

Step 2: Turn off the car engine and let it cool

If the weather is too hot, park the car under a shade and switch off the engine. Wait for the engine to cool down; this will take about 30 minutes or more, depending on the weather and the engine’s condition.

Step 3: Find the radiator or coolant reservoir

Open the car’s hood and find a white translucent container with tubes linking it to the radiator. It can be found in the grill at the front part of the engine. On it are markings that show the full range.

For more information on how to find the coolant reservoir and radiator, you can check the owner’s manual.

Step 4: Remove the radiator or coolant cap

Once you can find the coolant reservoir and radiator, the next step is to remove the coolant cap. In more modern vehicles, the coolant cap comes with a label. It makes it easier for people to locate the cap coolant reservoir and clears their doubts.

Now, you do not immediately remove the coolant cap; you need to ensure that the coolant is cool enough. Place your hands on the engine and the coolant cap; if it is still hot, wait for it to cool down.

However, if the engine is cool or slightly warm, loosen the coolant or radiator cap and wait. It releases every pressure trapped in the system. Avoid opening the cap too fast.

Place a thick piece of rag on the cap and unscrew it. Ensure that during this process, you wear a glove and goggles to protect against the pressure from the cooling system.

Step 5: Drain old coolant

Draining old coolant is not a mandatory step. If you feel that the coolant is dirty or contaminated or the coolant mix is not affected, then you should drain the coolant.

Below is how you can drain the coolant of your vehicle.

  • Lift the front of the vehicle with jack stands, then remove the radiator cap.
  • Locate the drain plug under the radiator, and unscrew it. Note that different drain plugs depend on the model of your vehicle. Check the vehicle manual to know what drain plug types to avoid damaging the plug and the coolant pan.
  • Ensure to have a new drain plug when changing the coolant oil. The plug could get damaged in the process of removing it.
  • Place a drain pan or disposable bucket beneath the drain plug and then remove the plug.
  • Allow the coolant to drain entirely into the drain, then go ahead to replace the coolant filter with a new one.

Step 6: Prepare your coolant

Coolant and antifreeze are not the same. Antifreeze is an important substance needed to make coolant. You get coolant when water is mixed with antifreeze in the appropriate ratio.

However, you do not always have to mix antifreeze with water to get coolant. There are products in sale that have already premixed the antifreeze with water.

Step 7: Add coolant to the engine

Once you have the right coolant check the coolant level on the reservoir container; if you drain the coolant, you do not check it; you have an empty coolant.

Place the funnel in the reservoir or radiator and pour the new coolant. Check the container markings while you pour the coolant and ensure that you fill till the coolant reaches below the max marking.

A popular question people ask is, “Do you add coolant to radiator or reservoir?” If the coolant is low, you should add coolant to the reservoir. However, if the reservoir is empty, add coolant directly to the radiator.

Also Read: How Long To Wait To Open Coolant Cap?

does the car need to be running when adding coolant

Does the car need to be running when adding coolant?

Should engine be running when you add coolant? The answer is no. Avoid opening the radiator or coolant reservoir cap when the engine is running.

Due to the pressure in the cooling system it could be dangerous to open the coolant cap and pour coolant. You stand the risk of being scorched by hot coolant as soon as the coolant cap is opened.

Whenever the question is, “Should your car be running when you add coolant?” understand that you will be putting yourself at harm’s way and could also damage the engine.

Another question people do ask is, “Does the car need to be running to add water?” The answer is still no. You will also harm yourself if you attempt to do this.


Should I add coolant while my car is off?

Yes, you should switch off the engine and wait about 30 minutes before opening the coolant cap and adding coolants. The engine needs to stay off because it builds up heat as the machine works. It then opens coolants for circulation. A lot of pressure is generated in this pressure, which could get pressure and coolants spraying out once the coolant cap is opened. 

How long should a car sit before adding coolant?

Once you switch off the engine, your vehicle should sit between 30 minutes to 1 hour before attempting to change the coolant. If the engine is overheating, it will take 2 to 3 hours to cool down completely. The temperature of the engine directly affects the cooling system. Until the engine is properly cool, you risk getting scorched if you open the coolant cap.

What happens if you put coolant in a hot car?

Adding coolant to a hot engine will crack the engine parts. The reason for this is when cold liquid comes in contact with hot metal, it causes to crack up. The sudden temperature change will cause the engine blocks and cylinder heads to crack. Also, the sudden temperature change will create a sudden burst of pressure from the cooling system that could burn your skin.

What if my coolant reservoir is empty?

Avoid adding coolant to a hot car, even with an empty reservoir. When you pour the coolant into the reservoir, it still finds its way to the engine. It will cause serious damage to the engine, costing thousands of dollars to fix. Also, the risk of being seriously injured is still there. The pressure from the coolant contacting the hot engine parts will send hot vapor and liquid through the coolant cap, causing serious skin burns.

How often should you top up coolant?

The coolant should be topped up whenever the coolant is low. This is why you must always check the coolant level before taking your vehicle for a drive. On the other hand, the coolant should be changed after a minimum of 30,000 miles. It depends on the age of the car. Newer vehicles may not need a coolant change until about 100,000 miles.

Final Words

If you encounter problems after adding coolant to the engine, like “car still overheating after adding coolant,” This could mean that the internal component in the cooling system is damaged or there is a leak. Ensure to have the issue checked by a professional before it gets any worse.

Akindayini Temiloluwa

I am passionate about everything automotive. Right from when I got my first toy car as a kid, I developed an interest in the inner workings of vehicles. As I grew up, my love for mechanical stuff became more substantial enough for me to pursue a career in it. My goal as an automotive content writer is to simplify the most challenging concepts for my readers, help them self-diagnose what may be wrong with their vehicles and offer real value for their time.

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