Car Engine Radiators Require Coolant, Not Just Water

Refilling the windshield washer system antifreeze

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A surprising number of people imagine that using pure water instead of a water/coolant mixture in a car radiator is fine if you live in a warm climate. After all, automotive coolant is generally known as "anti-freeze," and what is the point of using antifreeze if your automobile will never be driven in conditions below 32 degrees Fahrenheit?

This misconception is common, and it comes with substantial risks to the health of your engine. Once you understand what coolant actually does, you're unlikely to make the same mistake. 

What Is Coolant/Antifreeze?

Whether you know it as coolant or antifreeze, this product is really just an additive that when mixed with water serves to broaden the range at which that water will freeze and boil. Pure coolant has none of these properties, but it becomes a magical elixir for your engine's cooling system when it is mixed with water at a 50/50 ratio. In this ratio, the mixture will not freeze until temperatures reach minus 30 degrees F., and will not boil until 275 degrees F. or so. This property is very important to your engine's cooling system. 

The primary ingredients in coolant are ethylene glycol (EG) and/or propylene glycol (PG). These are the active ingredients that allow the coolant mixture to remain in liquid form over such a wide temperature range. To this, there are a number of additives and inhibitors added to the active ingredients.

Finally, there are dyes added to the coolant that give it a very bright color. The colors are quite striking and may be green, yellow, pink, orange, or red. These are intended to help identify the ingredients in the antifreeze so that you can use a product that is suited for the nature of your engine's cooling system. If you are changing coolant yourself, make sure to consult with a dealer or check the automobiles owner's manual for the recommended coolant. 

The Importance of Coolant for Your Engine

The core benefit of coolant for your car's cooling system lies in the fact that the mixture remains in liquid for such a wide temperature range. This means that in freezing weather conditions, the coolant will still be a liquid and can circulate effectively through the system to cool the engine and prevent damage. And in hot weather or when the car is being operated at peak load for long periods, the coolant will resist boiling and continue to circulate as a liquid, effectively cooling the engine. 

The additives in coolant are present primarily to prevent corrosion of the parts. And because the metals used in cooling systems differ from manufacturer to manufacturer, it's important to use a coolant suitable for your car. Although some coolants are marketed as universal products suitable for all cars, it's always best to check with the car manufacturer and make sure. 


  • If you are faced with low coolant levels in your car's radiator, do not just pour in pure coolant. For it to achieve its necessary thermal range, coolant must be mixed 50/50 with water. 
  • Ethylene glycol is extremely poisonous. Even worse, it is sweet to the taste. A child attracted to the liquid with its vibrant colors or an animal who laps up a spilled puddle of coolant is at dire risk. Propylene glycol is considerably less toxic, so if you're not able to safeguard the product, make sure to opt for a coolant based on PG. 
  • Follow your local guidelines for safe disposal of coolant. Normally this will mean bringing to your county's hazardous waste disposal facility. Local automotive service centers may be able to take it off your hands, sometimes for a small fee. If spills occur, soak them up with kitty litter and carefully sweep it up. 

Coolant/ Water Mixture, Not Just Water

The short answer is that it's a bad idea to pour pure water into your radiator, no matter what your climate conditions are. A proper coolant mixture is essential to the proper operation of your engine's cooling system and to its long life.