How to Add Coolant to Car

By: Kristen Hall-Geisler  | 
water to radiator
When your car overheats, you can add water to the radiator if you exercise some caution. GretaMarie/Getty Images

Owning your own vehicle can be a real quality of life enhancer. But with great power comes great responsibility, and regular maintenance. There are things drivers must know, including how to add coolant to car, how to change a flat, and up to date oil changes.

Yes, adding coolant is an essential car maintenance task that helps ensure your engine runs smoothly and prevents overheating. If you've ever watched the temperature gauge creep higher, you'll understand why.


An overheating car is not good, which is why every driver must take at least a little time to better understand how to protect it from happening.

What Is Engine Coolant?

Coolant, also known as antifreeze, is an essential fluid for your car's cooling system. It serves multiple essential functions that are vital for the smooth operation and longevity of your car's engine. Firstly, coolant is formulated to absorb heat that's generated by an engine during operation and dissipating it through the radiator. This process helps keep the engine at an optimal temperature and prevent overheating.

Coolant solution is a mixture of water and what's known as antifreeze compounds, which are typically ethylene glycol or propylene glycol and a blend of additives. The coolant's formulation gives it a lower freezing point and a higher boiling point than plain water, making it highly effective under a wide range of temperatures.


What Happens When You're Low on Coolant?

Running low on coolant can lead to a series of problems for your car that can affect it's performance and longevity, as well as the safety of all passengers. More specifically, here are a few things that can happen to a vehicle with a low coolant level:

  • Engine overheating: The most immediate effect of low coolant is engine overheating, which can cause the warping of engine components, head gasket failure, and even engine seizure [source: Nerad].
  • Poor heater performance: Coolant helps heat the cabin of your car too. A low coolant reservoir may result in a heating system that only blows cold air.
  • Increased engine wear: As mentioned above, coolant is loaded with additives designed to lubricate the moving parts within the cooling system. As such, low levels lead to more friction and wear on these parts.

Those are three highlights, but that's not even the whole picture. Other notable downsides of running low on coolant include decreased fuel efficiency and increased emissions. All of that is to say that drivers must do everything they can to keep their coolant reservoir full.


How to Add Coolant

Maintaining the correct level of coolant is crucial. Fortunately, you don't have to be an automotive genius to tackle the job yourself. All you need are a few widely available supplies and a step-by-step guide [source: Miller].

Materials needed:


  • A bottle of the correct type of coolant for your vehicle.
  • Distilled water (if your coolant needs to be diluted)
  • A funnel
  • Protective gloves and eyewear
  • A clean rag or paper towel

Step 1: Locate the Coolant Reservoir

The coolant reservoir is usually a transparent plastic container located near the radiator. It will often be labeled with the word "coolant" or have a symbol resembling a thermometer. For more specific instructions, refer to your vehicle's manual.

Step 2: Check the Coolant Level

Ensure your engine is off, and cool before removing the coolant reservoir cap. Remove the cap and check the fluid level against the fill line on the side of the reservoir. There should be a "full" or "max" line indicating the optimal level.

Step 3: Prepare the Coolant Mixture

If you're coolant needs to be mixed with water, prepare the mixture according to the manufacturer's recommendations. Typically this is a 50/50 mix of coolant and distilled water.

Step 4: Add Coolant

If the car's coolant level is low, use a funnel to pour the coolant into the reservoir until it reaches the fill line. DO not over fill, as coolant needs room to expand when it heats up.

Step 5: Replace the Cap and Clean Up

After adding the fresh coolant, securely replace the coolant cap on the reservoir and wipe away any spills to prevent damage.

Step 6: Check for Leaks

Start your engine and allow it to run for a few minutes with the heater set to the hottest setting. This will help circulate the coolant. Check under the car for any leaks. If you notice a leak, it's important to have your car inspected by a professional mechanic immediately.

Safety Tips:

  • Always check the coolant level when the engine is cool to avoid burns from hot coolant or steam.
  • Use the type of coolant recommended by your vehicle's manufacturer for optimal performance.
  • Dispose of used coolant properly, as it is toxic and can harm the environment.

Regularly checking and maintaining the coolant level in your car is essential for its performance and to prevent overheating. By following the steps outlined above, you can ensure your car's cooling system is in good condition. Remember to consult your vehicle's manual for specific recommendations and to wear protective gear when handling coolant.


Car Radiator FAQ

Can I use water instead of coolant?
Using a coolant in your vehicle’s radiator is best to prevent overheating. However, you can use water in a pinch if you don't have any. Just be mindful that water boils quicker than coolant, so you’ll want to change it out as soon as possible.
Where do I put water when my car overheats?
You need to put the water in the radiator by removing the pressure cap once your vehicle cools down. You can also add the water to the coolant reservoir or recovery tank if your car is overheating to the point where there’s steam.
What liquid is used in car radiators to prevent overheating?
Coolant is the most effective liquid used to prevent vehicles from overheating. You can use water as well in case of emergency or mix them using a 60/40 ratio.
What are the signs of low coolant?
All cars have an icon on their dashboard that indicates if it is overheating or low on coolant. Another sign of low coolant is steam coming out of the engine when you pop the hood. It’s best if you regularly check the level to be preventative.