How to Check & Top Up Coolant in Your Car

How to Check & Top Up Coolant in Your Car

Checking and topping up your car’s coolant is one of the fundamental things you learn regarding car maintenance and repair. Although most car owners already know how to do this, not everybody is aware of some preventive measures or causes for rapidly dropping coolant levels.

Coolant levels may be checked through the coolant reservoir and the radiator itself. Minimum and maximum markings on the reservoir indicate where coolant levels should ideally be. Topping it up will require a cool engine and the right type of coolant.

If you are keen on learning more about checking and topping up coolants, coolant types, preventive measures, and even troubleshooting possible problems in your cooling system to reduce the amount of money you spend on a car service and repair at your local dealership, then continue reading below.

What Is Coolant & What Does It Do?

Car coolants are a mixture of water and certain chemicals to prevent overheating and corrosion inside a motor vehicle’s engine, among others. They also lubricate the mechanically moving parts that it comes into contact with.

Every commercially available automotive coolant is Glycol-based and is mostly a mixture of Ethylene Glycol with water and other additive packages. Another type of glycol-based coolant contains Propylene glycol and water instead. The only difference between the two is that the latter is less toxic.

Coolants work by transferring heat and adding antifreeze protection to a motor vehicle’s engine, preventing encumbrances caused by corrosion and other factors. To understand why coolants are essential, it is important to understand how motor vehicle engines work. Energy is created by internal combustion engines by burning fuel, with some of the energy utilised by the engine which consequently moves the vehicle forward. However, a portion of this energy is converted into heat.

A relatively moderate number of motor vehicle engine failures are a result of overheating or engine cooling issues. Coolants are essential in maintaining a motor vehicle’s reliability and performance.

Car coolants are situated within a reservoir attached to the radiator before being sent to the engine block and related components. These coolants are used simultaneously and in conjunction with the motor vehicle’s liquid cooling system and are made of several components; the water/ coolant pump is in charge of circulating coolant throughout the system, and the radiator pulls heat away from the coolant while the radiator hoses connect key parts of the cooling system together.

The kinds of coolants used in automobile cooling systems are:

  1. Inorganic Acid Technology Coolant (IAT) – The conventional coolant widely used in order vehicles back in the day. It requires a higher frequency of changing due to its weaker qualities. It comes in either green or yellow colours.
  2. Organic Acid Technology Coolant (OAT) – The more common type of coolant nowadays, which has relatively better qualities than its conventional sibling. It comes in many colours, including dark green, orange, blue, and pink.
  3. Hybrid Organic Acid Technology Coolant (HOAT) – As the name suggests, it is a hybrid of IAT and OAT. It has continually proven to be the most popular coolant in newer and modern vehicles.

Remember that not all cars can use every type of coolant. Check your car’s owner’s manual to ensure that your car will not malfunction due to the use of wrong or incompatible coolant.

Is Coolant the Same as Antifreeze?

Although similar, coolant is the result of antifreeze that has been diluted with water to be used in engine cooling systems. Mixing water with antifreeze to make coolant gives the liquid a higher boiling point and a lower freezing point, making it more resilient to extreme temperatures.  

A ‘coolant’ generally contains a 50-50 mix of antifreeze and water, or up to 70% antifreeze for vehicles that operate under extremely cold temperatures. But the 50-50 mixture will usually provide just enough cooling for most use case scenarios.

How Do I Know if My Coolant Is Low?

The most common sign that your coolant is low is an indicator light on your dashboard is illuminated. However, as standard car care, you should check your coolant levels at least every two or three weeks and top it up before your car tells you its levels are low. 

The following are the most common symptoms of having low coolant levels:

  • High-Temperature Gauge near the red – Arguably, the definitive sign of low coolant levels is the high-temperature gauge on the dashboard near or at the red, which indicates that the engine is too hot. Usually, the gauge stays between the “H” and “C” icons. Once the gauge indicates your engine is getting too hot, with the needle moving towards the “H”, it is time to stop your engine and have it towed for necessary repairs.
  • Air Conditioning System Malfunctioning – Once the air coming out of your automobile’s air conditioning system begins to feel hot, chances are the coolant levels are too low.
  • ‘Sweet’ odour inside the automobile – Coolant leaks are characterised by the sweet odour it produces. This odour can usually be found inside the air conditioning system itself or under the hood. The odour is caused by the Glycol base of the coolant. Remember that although weird or abnormal odours are usually a sign of something wrong, they may not always be a clear indicator, so consult with a mechanic or professional to be sure.

It should be worth noting that there are also cases in which the coolant level sensor itself is faulty, which lights up the dashboard’s coolant light despite having sufficient coolant levels. So diagnosing your car’s problems by yourself may not always be the best idea.

How Often Should I Check My Car’s Coolant Levels?

You should check your car’s coolant levels regularly, at least every three weeks, before or after a long trip. You should also make it a habit to check coolant levels during or after a trip outside your vehicle’s normal circumstances, such as making a long trip during an extremely hot day.

Remember that when checking your car’s coolant levels, it’s best to go the extra mile to check for abnormalities. Simply checking whether the low coolant indicator light is on or off on your dashboard or the reservoir does not rule out possible leaks or other related problems. Doing so will save you money from towing services and keep your car in good condition. 

If you have a car maintenance checklist that you go over monthly, you can add checking coolant levels to it to ensure it’s getting checked frequently. 

How Do I Check the Coolant Level in My Car?

To check the coolant level in your car, follow these steps:

  1. Let the Engine Cool – Before inspecting your car’s cooling system, ensure the engine is cool. This means you shouldn’t be checking the coolant levels immediately after turning off the engine. Give it a few hours of rest and cooldown time so you aren’t sprayed with hot coolant when you open the radiator cap. You can also refer to your car’s manual, as some vehicles may have extra steps for checking coolant levels.
  2. Locate the Coolant Reservoir – Inspect your car’s plastic overflow bottle, which is connected to the cooling system. You will usually see markings on the side that indicate low or high levels of coolant, which should be enough to tell you whether you need to add more coolant or not. Ideally, the coolant should always be somewhere between the markings but never under the low marking.
  3. Top Up Your Coolant Levels – Should coolant levels be low, refer to your car’s owner manual to ensure that you use the correct type of coolant and the proper way of topping it up. When unsure, contact your car’s manufacturer or your trusted mechanic.

This process is similar to how to check your transmission fluid, and only takes a few minutes. By checking your coolant and transmission fluid levels at the same time, following similar steps, you can ensure your car has good levels of vital fluids. 

Do You Check Coolant Level Hot or Cold?

Always check coolant levels when they are cold. Hot coolant won’t give you accurate readings and, in some cases, can shoot out right after opening the cap and cause severe burns. 

Always check coolant levels before driving or after giving your car a few hours of rest.

Why Is My Coolant Low?

Other than driving in extreme temperatures, coolant is usually only lowered by leaks in the engine system caused by pressure loss or damage. Coolant does not generally require replacement since it works inside a closed system. As such, leaks are the most common reason for low coolant levels.

Below are some of the ways coolant fluid may leak:

  • External Leaks – These leaks stem from the connection between hoses, from the radiator hoses, or the radiator itself.
  • Radiator Cap Leaks – This type of leak occurs when the radiator cap’s seal is broken, causing pressurised coolant to leak out. 
  • Internal Leaks – This type of leak is any place within the system where the coolant fluid may leak out, like the head gasket of the engine.

As with everything in this article, the information is meant to be a guide, not a complete troubleshooting and repair tutorial. It is highly recommended that you consult a mechanic or a professional for any problem.

Do Cars Lose Coolant Over Time?

Yes. Although the closed system minimises the evaporation rate, dry climates and high coolant temperatures can cause it to evaporate, albeit at a very slow rate. This is why it is advised to check coolant levels regularly so that you may fix the problem as soon as it shows.

In addition, extremely cold ambient temperatures cause coolant liquid to contract. This, in turn, shows a drop in the coolant level, which will eventually revert back after the temperature warms up.

Why Does My Coolant Run Out Fast?

The most common cause of losing coolant quickly is some kind of leak in between the radiator hoses, the radiator cap, or within the cooling system itself. Another is that the coolant levels are evaporating too quickly, caused by driving in hot weather conditions or a related problem within your car’s cooling system.

What Should I Do if My Coolant Is Low?

If your coolant levels are low, ensure it is replenished accordingly with the correct type of coolant before using your car. Driving with low coolant levels increases the risk of overheating, damaging your car’s internals, which is detrimental to its overall condition. 

How to Top Up Coolant

  1. Let Your Engine Cool – Make sure your engine is cool. Give your car a few hours of rest right after driving before topping up the coolant. This ensures that the coolant has cooled down and is ready to be mixed with room temperature coolant.
  2. Locate the Coolant Reservoir – The coolant reservoir often looks like a clear plastic tub containing coloured liquid (the coolant itself) inside. The cap has a warning label with ‘Caution’ or ‘Hot’.
  3. Check the Coolant Levels – Ensure the coolant level is low enough before topping up. You wouldn’t want to fill the reservoir beyond its indicated maximum levels. Remove the cap and assess the levels.
  4. Dilute Pure Coolant – If you use pure coolant, it will have to be mixed with distilled water first. A safe mixture is 50% distilled water and 50% coolant. If you do not have distilled water readily available, you can boil some water and use it after it cools down.
  5. Fill Up The Coolant Reservoir – If there is no longer any coolant liquid inside the radiator, open the cap and top it up until you can see coolant just below the neck. Just like the radiator, the coolant reservoir has indicators for the minimum and maximum levels. Pour the coolant until it reaches the maximum line, or just before it does, then put the cap back on.

Can You Just Top Up Coolant?

Yes, you can top up without flushing or draining the remaining coolant so long as you use the same colour of coolant in the reservoir. Most cooling systems in modern cards do not require flushing or draining and can simply be added to when coolant levels are low.

Do You Add Coolant to Radiator or Reservoir?

Coolant should be added to the reservoir, not the radiator itself. The radiator is the component through which the coolant flows, dissipating heat. The coolant reservoir, which is connected to the cooling system, is where the coolant sits. 

How Much Coolant Does a Car Need?

The average car can easily hold over five litres of coolant. However, unless your coolant reservoir is completely empty, you won’t need to buy that much to top up your coolant levels. Usually, when topping up coolant, adding a litre should bring your levels close to the maximum amount indicated on the reservoir. 

Can I Use Water Instead of Coolant?

You cannot run your car with water instead of coolant, as the water will quickly evaporate, leaving the reservoir empty, damaging your car. However, water can be used in emergencies to top up your car if your coolant levels are very low and you have no way of getting coolant. 

When Should I Drain & Replace My Coolant?

Depending on the vehicle type, size, and manufacturer, the average duration between coolant flushes should ideally be two years or every 30,000 miles for silicate coolants. This increases to five years or every 100,000 miles for extended drain coolants.

How Long After Adding Coolant Can I Drive?

It highly depends on how much coolant is being added or if the coolant is being replaced in its entirety. However, a good rule of thumb is to wait for at least 15 minutes before driving off. This will allow the hood, engine, and coolant to cool down.


This article is published in good faith and for general informational purposes only. Shift Automotive does not make any warranties about the ongoing completeness and reliability of this information, and specifics will vary according to your vehicle’s manufacturer and model. This article is not intended to replace consultation with a qualified automotive service technician.