Car Repair and Maintenance

Adding Coolant to a Car Beginner’s Guide [6 Steps]

One of the most crucial maintenance is checking and adding coolant to a car. Coolant is important in a car because it makes the radiator cool down the engine to prevent overheating. When the engine is running, opening the radiator cap might result in coolant and steam shooting out, which can cause serious burns.

Additionally, you can add too much or too little coolant since you can’t see the exact quantity of fluid in the vehicle while the engine is running. In this article, you will learn everything about adding coolant to your car including questions like does the car need to be running when adding coolant and so much more.

adding coolant to a car

How does coolant work?

To reduce its freezing point, glycol is often added to water to create coolant. This prevents the cooling system in the car from freezing during the winter. A dye and other chemicals that lubricate the engine components and lessen the chance of rust and corrosion in the radiator are also included in the fluid.

The radiator of the car uses coolant to cool down the engine and prevent overheating. The thermostatic valve in the cooler, which is a radiator, keeps track of the vehicle’s temperature.

The radiator releases coolant into the engine to lower its temperature once it reaches a specific point. The liquid is cooled when the coolant is returned to the radiator. The airflow created while the car is moving quickly is one method of cooling.

Steps to adding coolant to a car

Be careful to mix coolant and water before adding coolant to your car (preferably demineralized). Before filling, it is a good idea to mix the liquid in the container.

Make sure the car has cooled down before adding the coolant. The coolant reservoir may grow if the car is heated because the cooling system is pressurized. As a result, it will be impossible for you to determine how much liquid to add to the reservoir.

You run the danger of being burnt when the pressure is released if you open the reservoir while the engine is still hot. For this reason, you must always wait until your car has cooled before adding coolant.

  1. Locate the coolant reservoir:

    It is usually found near the radiator and is clearly labeled. The coolant reservoir is found close to the radiator and well-labeled to avoid a mix up. It is completely different from the wiper washer and radiator.

  2. Check the level of the coolant

    by looking at the side of the reservoir. If it’s low, go to the next step. If the coolant level is empty or low.

  3. Add coolant.

    Pour the coolant into the reservoir using a funnel. Be careful not to put too much in.

  4. Check for leaks:

    Turn the car off and look for coolant leaks around the coolant reservoir or the hoses going to the radiator.

  5. Start the engine.

    Turn on the engine and let it run for a few minutes so that the coolant can move around the system.

  6. Again, check the level:

    Wait for the engine to cool down, then check the level of coolant again and, if needed, add more.

Note: Always use the recommended coolant type for your vehicle, using the wrong type can cause damage to the engine.

Does the car need to be running when adding coolant?

Coolant preserves and sustains a steady temperature in your car’s engine by sending it through and taking away excess heat. Consequently, it may seem like the car needs to be running when adding coolant; meanwhile, that is not the case.

To answer the question, your car should not be running when adding cooling. This is because whenever your car engine is hot, there is every chance that you could burn yourself or pour in the wrong amount of coolant. Therefore, a hot engine can make the coolant expand, causing problems with the level reading. This is why you should ensure your engine is switched off and cool before you add coolant.

Adding coolant to a car requires you to remove the radiator cap and open the coolant reservoir and all these can’t be done while the car is running.

Note also that the ignition system works at a very high and hazardous voltage. Thus, your car’s electrical system has to be in ignition position 0 when working in the engine compartment, Volvo advises.

How long to run the engine after adding coolant?

The time frame to run a car engine after adding coolant is dependent on the type of coolant you used.

For example, if you used plain water, you should run the car for at least 30 minutes while the radiator cap is off to ensure the entire air runs away from the system.

Can I drive right after adding coolant?

Yes. You can run your car after adding coolant for some minutes while you inspect your car for leaks beneath the engine. As a result, running your car after adding coolant removes any air bubbles in the cooling system.

Once done, turn off the car ignition and add more coolant if needed. Then run the car once more for a few minutes and check for any leaks.

When adding coolant to a car, ensure it is spread through the engine and you do not see any air bubbles in the system.

If you add coolant to a hot engine, that can be dangerous. Corrosion and cracking may occur when the coolant comes into contact with a hot engine. Leaks from engine cracks can also result in overheating and ultimately seizing of the engine.

How long should the engine be off before adding coolant?

The ideal time to add any coolant is at least 30 minutes after the engine has been switched off. Wait until the radiator is cool to the touch if you don’t have that much time.

No, a heated engine should never have coolant added to it. A heated engine’s hot metal quickly contracts when a cold liquid is injected, breaking the engine block.

Since the coolant expands due to heat, adding more while the engine is running might result in an overflow. Open the radiator cap and add extra fluid only when the vehicle has cooled down.

How often should I add coolant?

It’s ideal to check the coolant level in your vehicle at least once a month, and more often if you see the temperature gauge starting to rise. If you have to add coolant regularly, there can be a system leak that has to be corrected.

Now, how do I know if my car needs coolant? Overheating is the main sign of a coolant leak. Pull over and inspect beneath the hood if your vehicle begins to run hot or if the temperature indicator on your display reads higher than usual.

Keep an eye out for any leaks that may have occurred, such as moisture around hoses or pools of fluid on the ground under the car. Low coolant levels, steam pouring from beneath the hood, and decreased engine performance are some further signs of a coolant leak.

Why do I have to keep topping up my coolant?

There are a few possible reasons why you may need to top up your coolant often. Even while there may not be any obvious trickling, a little leak might nonetheless let enough fluid out that you must constantly top it up.

If the coolant is boiling away and producing steam, there is a deeper issue. This can be the result of a broken radiator cap or a water pump issue. In either scenario, it’s important to have a professional examine your vehicle right away.

Should I put coolant in my radiator or reservoir?

It’s crucial to understand where your car’s coolant travels. Your vehicle will either have a radiator or a reservoir, depending on the make and type. A reservoir is often found in the front of the engine compartment on the majority of vehicles produced after 2005. Typically, the radiator is situated near the rear of the engine compartment.

If you have a radiator, you need to fill it with coolant. If you have a reservoir, you ought to fill it with coolant. Coolant should never be added directly to the engine.

Can low coolant cause rough idle?

Yes, a low coolant level might contribute to a harsh idle in your car. Your engine’s lack of coolant prevents it from adequately lubricating the moving components.

Increased heat and friction from this might harm the engine and make it perform erratically. Make careful to add additional coolant as soon as you can if you find your car’s level is low.

Meanwhile, can you drive with a low coolant level? Driving with low coolant levels is not advised. Check the coolant level if your vehicle begins to overheat and then pull over. Add extra if necessary and carry on if it’s low. The engine can be irreparably harmed if it overheats once more.

Also, your coolant can sometimes be low but no leaks. Your coolant level might be low but no leaks.

  • Evaporation is the most typical explanation. Water is included in the coolant, and as time passes, it will evaporate from the mixture. You may need to add coolant more regularly to maintain the level topped up if you live in a hot environment or use your car a lot in hot weather.
  • A broken radiator cap is another typical cause of a low coolant level without leaks. The radiator cap’s purpose is to prevent coolant leakage and retain it within the radiator.
  • Coolant may leak from the system if the pressure release valve is malfunctioning. Replace your radiator cap if you think it’s not working correctly.
  • Another explanation for a low coolant level and no leaks might be a tiny, imperceptible leak in the cooling system. Because they often occur at system joints or connections, coolant leaks may be exceedingly difficult to detect.

A leak can go undetected until the coolant has accumulated on the ground or until you realize your coolant level is low.


Adding coolant while the engine is cold is the ideal option you should take. You won’t be burnt by the hot coolant or steam if you do this. When the engine is off, it is also easier to observe the radiator’s coolant level.

You should never add coolant to the engine itself. If you have a radiator, fill it with coolant. If you have a reservoir, fill it with coolant. Make sure the engine is running for a while after adding coolant so that the coolant can circulate. By doing this, you can find any possible system leaks.



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Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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