coolant in overflow tank

Coolant In The Overflow Tank – The Right Amount You Need

An engine coolant is responsible for protecting the radiator when you park or drive your car in extreme temperatures. 

Driving a car is all fun and games but maintaining a car is a different ball game altogether. As a car owner, you might have thought about questions like how much coolant should be in the overflow tank? To answer this simply, let’s say that you should fill the coolant to the mark that says maximum or full on the overflow tank.

In this article, you will learn the significance of the coolant and how much coolant should be there in the overflow tank. Let us build our base first.

What is a Coolant?

A coolant or antifreeze is a mixture of water and glycol. Its primary function is to make sure that your car’s engine works in extreme temperatures. It protects your vehicle’s engine against overheating in hot weather and prevents it from freezing in cold weather. Check out this guide on how to stop antifreeze leak.

Coolant also protects the components of your engine against corrosion. Corrosion in the engine results in several problems. In the long run, it reduces the efficiency of the engine as well.

What is the Right Amount of Coolant?

An overflow tank, also known as a coolant reservoir, is usually the transparent plastic container next to the radiator. A coolant is not directly poured into the radiator, opposed to what most people think. 

Through the cap on the reservoir, you can see the coolant inside. On the reservoir, you will find marks or levels indicating the following:

  • Minimum/Low
  • Maximum/Full

As shown in the image below

These marks on the reservoir indicate the required level of a coolant. Make sure you fill the coolant to till maximum or the full level marked on the reservoir.

There might be space above the maximum or full mark, but you should refrain from filling up that space with the coolant. The coolant expands when it’s heated and contracts when it’s cool.

The extra space above the maximum/full mark gives room to the coolant to expand when the engine gets hot. When the engine gets cold, we consider the minimum or the low mark. When the engine is heated, we consider the maximum or the full mark.

Overfilling the reservoir will cause damage to the engine and might result in blowback.

There are few things we would like you to make a note of while filling a coolant:

  • Make sure you do not add extra coolant to the overflow tank when the engine is hot.
  • Do not mix two different colors of coolant.
  • Avoid opening the reservoir cap if it’s hot. 

What are the Components of a Coolant?

So far, we have understood that a coolant is imperative to keep the car’s engine up and to run. Let us understand what the components of a coolant are.

Glycol is the main component in all automotive coolants. A coolant is made by mixing equal parts of water and ethylene glycol. Some coolants also consist of propylene glycol and water.

The difference between a coolant made of ethylene and propylene is that propylene is less toxic. 

Pure water is an excellent heat carrier. So why do you need to add glycol at all? Well, the answer to this is simple. Water comes with other challenges. It may provide excellent transferring capabilities, but it also causes corrosion. 

A coolant made out of pure water will carry rust and heat and further damage the cooling system.

Type of Coolants

As there are many variants of coolants available in the market, you must understand the various coolant types. We strongly suggest you read reviews about coolants’ to make an informed choice.

Let us dive into the different types of coolants.

  • Organic Acid Technology (IAT) Coolant: Several brands deal with organic acid technology coolant. It’s widely available in many colors like such as dark green, pink, and orange.
  • Inorganic Acid Technology (OAT) Coolant: Mechanics widely used this conventional coolant in older cards. This variant needs to be refilled or changed as it loses its attributes soon.
  • Hybrid Organic Acid Technology Coolant: As the name suggests, this coolant is a hybrid of inorganic acid technology and organic acid technology. The majority of new vehicles use it. 

Different coolants fulfill different functions.

What causes the coolant to leak?

A coolant can leak due to several reasons. First things first, let us try and understand how you can detect a coolant leak.

Check your engine for overheating

A common indicator of a coolant leak is an overheated car. If you notice the temperature of your car’s engine is higher than what it usually is, you should stop your vehicle right away. Allow the engine to cool down before you hit the road again.

The easiest way to check for a coolant leak is to look for drip marks under the car. If you have parked your car for a long time, check for colored drip marks. You can detect a coolant easily as they have a sweet scent.

If you notice any such drip marks, you should immediately consult a mechanic.

Common causes behind a coolant leak

  • A Bad Radiator Cap

A coolant goes through the radiator to the car’s engine and travels back from the engine to the radiator, carrying heat. Consequently, this traveling of the coolant can cause wear and tear in the radiator. As the coolant is partly water, it can also cause corrosion.

The sediments from the corrosion and the wear and tear can damage the radiator cap and further cause a leak.

  • A Faulty Water Pump

A water pump helps to circulate the coolant throughout the car and maintain an optimum temperature. A damaged pump or a worn-out seal can result in a leak. A faulty water pump will result in a decline of circulation or no circulation at all.

Your engine tends to get heated without a proper circulation of a coolant. As a result, it can cause severe damage to the engine. 

  • A Broken Head Gasket

A head gasket can get damaged over time and use. A head gasket supports the functions of the engine and keeps it healthy. A blown head gasket or a head gasket with a leak will cause your coolant and engine oil to mix.

A leak in a head gasket will cause the engine to heat up and eventually result in engine sputter and seizure

  • A Faulty Overflow Tank

As we have established, the plastic container where you pour coolant is called the reservoir or the overflow tank. As the tank is made up of plastic, it can weaken over time. The tank or its supported components can develop a crack.

The coolant can escape through the cracks and cause a leak.

The Bottom Line

Coolants play a vital role in the smooth functioning of your vehicle’s engine. You must consider both the quality and the quantity of the coolant in your vehicle. Moreover, make sure you take specific steps to prevent any leaks. 

 The best way to avoid a coolant leak is to set regular appointments with the mechanic. As time passes, one or another component suffers damage due to wear and tear. Make a schedule and ensure that you take your car to a professional and trusted mechanic. 

There are plenty of ways that you keep a check to avoid any leakages at your end. Pay attention to your car’s temperature as you indulge in long drives. Also, learn why your CV joints are making noise while driving.

An old coolant can become acidic. Eventually, it can cause damage to the overflow tank and its components. Make sure that the coolant sitting in your overflow tank is not old. Such steps will prevent damage to your vehicle.


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