Do You Add Coolant to Radiator or Reservoir

If your vehicle needs extra coolant, you may be wondering do you add coolant to radiator or reservoir in your vehicle.

This is a commonly asked question, as a lot of people do not know where exactly the coolant goes.

Automobile coolant

The reservoir and radiator have similar functions, and you may have heard about using one or the other for your coolant. Making it complicated if you are not necessarily an expert in vehicles and do not know where the coolant should go.

Using a coolant is important for your vehicle as it helps to keep the temperature even, allowing your vehicle to run optimally. Because of this, you should figure out where the coolant goes in your vehicle, so that you can add coolant when necessary.

Keep reading to find out where the coolant should go in your vehicle and whether or not the reservoir or the radiator is the ideal place.

You Can Add Coolant to a Reservoir or Radiator

If you need to add coolant to your vehicle, you may be wondering do you add coolant to radiator or reservoir. This is a good question to ask, as some people may not know that you can add coolant to a reservoir or a radiator.

For the most part, you can add coolant to either the reservoir or the radio of your vehicle quite easily. They are both able to take on the coolant depending on why you choose which option.

There are different instances where adding a coolant to the radiator may be better than doing it to the reservoir and vice versa. This can also depend on how old your vehicle is, as some older vehicles do better with the coolant going into the radiator

So there are multiple different factors to consider when looking into where you should add the coolant for your vehicle. As the reservoir or the radiator may be better depending on your vehicle and how long you have waited to add coolant.


For the most part, the reservoir is the ideal place to add the coolant to any type of vehicle. This is an area designed specifically for the coolant, and this is where it should go ideally if possible.

Though you should not pour the coolant into the reservoir directly if the reservoir is completely empty. This can be damaging, and it would be much better to pour the coolant into the radiator instead.


You can often pour coolant into the radiator if you want to, but there are certain instances where this will be necessary. You should always pour coolant into the radiator if your reservoir is completely empty.

You should also do this if your vehicle is older, as the radiator is more suitable for coolant and old vehicles. One time that you should not pour coolant into your radiator is if it already contains a lot of water.

Too much water mixed with the coolant can create a build-up within the radiator and lead to problems down the road.

You Can Add New Coolant Without Flushing the Old Coolant

Another question that drivers may have is if they need to flush the old coolant before they add a new coolant. The good news is that this is not necessary, as you can add new coolant to old coolant without issues.

The only thing you should take into consideration is just how old the original coolant is. As coolant will eventually start to become acidic the longer it sits in your vehicle without being flushed.

This can lead to corrosion and result in issues with your cooling system and your radiator and reservoir. So if the coolant in your vehicle is on the old side, you should flush it before adding a new coolant to prevent it from becoming acidic.

You Should Add Diluted Coolant to a Radiator

Another question that you may have is if your coolant needs to be diluted before adding it to your radiator. The majority of coolant that you buy is going to already be diluted with water to 50-50 percent.

This is important as the water helps to balance out the coolant and produce a fluid that has a good boiling point that won’t get too hot. This allows the coolant to properly cool down your engine and your cooling system so that your vehicle can run smoothly.

Some people decide to buy more condensed coolants or make their own coolant, so you will need to dilute it yourself. You can add undiluted coolant to your radiator, but it is not going to be nearly as efficient.

It will not be able to do its job properly and can result in your vehicle not being cooled the way it needs to be. Which can lead to more serious auto issues later on down the road if you continue to use undiluted coolant.

That is why it’s generally best for drivers to simply buy coolant from a store that has already been diluted. As you want it to be diluted in the right amount in order for it to work correctly, as too much water is just as bad as too much coolant.

Coolant Should be Filled to the Max Reservoir Line

When you are adding coolant to the reservoir of your vehicle, it is important to not overfill it. You will see a max line in the reservoir that lets you know how high the coolant should be.

You should not exceed this line as that will be too much coolant and can lead to issues or overspilling. This line also makes it helpful when topping off your coolant so that your vehicle always has a generous supply.

That is why most people choose to pour their coolant into the reservoir if they need to top it off here and there. You should not do this if your reservoir is empty, but it is a good place to add the coolant if you need a little extra.

The line provides an easy-to-follow guide so that you know exactly how much coolant you need and when you need it.