One of the most important yet easy tasks you can learn, as a driver and car owner, is how to add engine coolant to your car.

Important because a lack of engine coolant can cause serious damage to the engine. Easy because it’s essentially a simple refill job.

This article will hopefully help you learn how to do this and show that you shouldn’t be reluctant to do it at all. On the contrary.

Besisdes this, lower in the article you can find some of the most asked questions regarding this topic.




Do not do this when the engine is hot!

When it is, sudden opening of the expansion tank may lead to a „geyser“ effect. Boiling hot coolant may end up on your hands or body causing severe burns.

So, if the engine is hot, open the hood and wait until it cools down. If you don’t have the time you’ll have to wait at least until it’s warm.

If the engine is already cold, proceed to the next step.




This is the first step in order to learn how to add engine coolant to your car.

Once the hood is up, search for the plastic expansion tank. This is the place where the coolant is supposed to be added.

It may be somewhat of a problem to find the expansion tank, especially for inexperienced drivers. You’ll see at least four different containers with caps of different colors and markings.

The cap on the expansion tank is usually blue, black, or yellow with a steam icon imprinted on it. Besides this, it usually has a written message that the coolant is hot or under pressure.

You’ll also see rubber hoses attached as well as a minimum and maximum level gauge imprinted on it.

The most common mistake drivers make is mixing up the expansion tank and the windshield washer fluid container. But if you pay at least some attention, you won’t make this mistake for sure.

On some cars (mostly older models) coolant can be added through the radiator by opening a metal cap located on top of it. The principle is the same. The only difference is where you add the coolant.




Turn the coolant cap counterclockwise and set it aside.

It may put up some resistance, especially if the expansion tank isn’t opened for a long time.

Take it easy, so you don’t tear the rubber gasket on the cap.




Pour coolant until it reaches the middle between minimum and maximum. Don’t overfill as this can cause excessive pressure build-up in the coolant system.

If you accidentally do, don’t worry. You can use a coolant gauge or a suction tool to remove the excess coolant.

Sometimes the expansion tank can be blurry making it hard to see the coolant level.  Then budge the car a bit backward and forwards so the coolant splashes a bit. It will make noticing much easier.

Besides knowing how to add engine coolant to your car, it’s also very important to know what coolant is inside the system. Mainly in terms of type, characteristics, and preferably from what manufacturer.

You should avoid mixing different coolants. This is best avoided by paying attention to the color of the coolant (like green, yellow, pink, or else).

When you don’t have the same one, it’s maybe better to add some distilled water to avoid causing damage to the system. Just have in mind if you do this that you’ll have to replace the coolant before winter as it becomes less freeze resistant.

Also, make sure not to add 100 percent antifreeze. It has to be diluted with water first and then added.




Return the cap and tighten clockwise. Watch that it sits in place properly so you don’t damage the plastic thread or rubber gasket.

Most caps „click“ when they reach the end so you’ll know it’s enough turning and that it’s properly tightened.

Some caps don’t have a thread but a locking-type system so pressing and turning once is enough.

Once you’ve finished, you can start the car and let the engine run for a couple of minutes so the coolant can circulate.

After that, check the coolant level again, if it’s OK then the job is finished.

You can also take a glance at the temperature gauge if the values are normal and the coolant cap also for any possible leaks.

But if everything was OK before adding the coolant, then it should be OK afterward.



The usual tell-tale signs are:

  • A mild increase in engine temperature
  • A low coolant level in the expansion tank
  • Weak cabin heating

In order to notice the low coolant level, you must make checkups on your car a regular habit. Click here if you’re interested in how to do that or watch our YouTube video (6:49-coolant check up part).




Besides knowing how to add engine coolant to your car, it’s good to know how much you should wait before adding some.

As mentioned, best to wait until the engine completely cools down. Then you’re certainly safe from any kind of burns or injuries.

A big help is opening the hood as it will seriously speed up the cooling process.

To be more specific on this topic:

  • A hot engine in the summer (with the hood up): wait at least an hour
  • A hot engine in the winter (with the hood up): about half an hour
  • Warm engine: you can add coolant immediately but be careful when opening the expansion tank

Take all of this with a grain of salt as it all depends on the outside temperature as well if the car has, for instance, overheated.

If you want to read more about the most common reasons for overheating, click here.



Regarding the engine, yes. Regarding your safety no.

The sooner the engine gets the needed coolant the better, this is true. Is it worth risking your hands and body and getting severely burned? I don’t think so.

However, if a dire situation demands it, there is a way. This is all under the condition that the coolant system hasn’t already overheated and that there isn’t any major flaw with it.

The procedure for when the engine is turned off but is still hot:

  • Wait a couple of minutes for the coolant pressure to reside before opening
  • Open the coolant cap slowly turning it counterclockwise. You’ll hear a hissing sound, this is steam coming out of the system.
  • Stop turning the cap any further until the hissing stops. After this continue opening but with caution. Imagine opening a bottle of soda under pressure. It’s basically the same.

Turning the coolant cap slowly has one more big benefit. If you see coolant gushing out when turning the coolant cap, you’ll have time to move away and save your hands from getting burned. When this the case, you’ll have to wait for the engine to cool down to continue.

When the engine is running:

Best use this only in case of an emergency (for instance, in a long uphill drive the coolant level runs low and overheating is imminent).

  • Park the car and don’t turn off the engine. Let it idle.
  • Slowly turn the coolant cap open. If everything is OK with the coolant system, you’ll just hear a small hissing sound. Once it stops, open the expansion tank.
  • Add coolant until you reach the needed level.

The point is that while the system is working, there isn’t much pressure within the tank itself.

While pouring, you’ll see a mild stream of coolant returning into the expansion tank. This is normal just watch your hands.



Hopefully, after reading all of this, you’ve seen that learning how to add coolant to your car is very simple. No more complicated than checking the oil, for instance.

Open the expansion tank, pour coolant until the level is between minimum and maximum. After that, return the cap and tighten it.

The best time to do this is when the car isn’t driven for a longer period of time (like in the morning or on weekends). This also a good opportunity to make all of the other necessary checkups.

When the engine is hot, if possible, wait for it to cool down. Especially do this if an engine overheating happens. Safety comes first before anything.

Having some spare coolant around the house or in the trunk is also good. It’s best to have the same as the one in your car’s coolant system.

In the end, this knowledge comes in handy when you’re on the road. Instead of waiting for someone to help you or risk engine overheating, you can solve the problem yourself.


Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for


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