How to Mix Car Coolant

by Contributor

On its own, coolant helps your car flush built-up heat out of its radiator to prevent your car from overheating. However, if you mix coolant with water in the proper ratio, you can also reap the benefits of the coolant's or antifreeze's anti-corrosive properties. You'll need to consult your car's owner's manual to learn the proper specifications for use of antifreeze or coolant, but there are several general principles to keep in mind when you mix car coolant with water.

Step 1

Consult your car's manual. There will be a section dedicated to coolant or antifreeze-usage specifications. If you cannot find this information, contact your car's manufacturer to learn the specs you need to know before proceeding.

Step 2

Stick to brand-name coolants, such as Prestone and ThermalTake.

Step 3

Mix your antifreeze at a one-to-one ratio with water. For temperate climates, this will provide the protection you need in winter weather and effectively work to keep your engine from overheating. In addition, a 50/50 coolant-to-water ratio fights rust, boiling and engine corrosion.

Step 4

Mix an ethylene-glycol coolant with water in a 70:30 ratio (in other words, 70-percent coolant to 30-percent water). This is recommended if you live in an environment that experiences harsh winter weather. It is also the highest coolant-to-water ratio that most experts recommend for use in car engines.

Step 5

Combine factory antifreeze or coolant products, such as DEX-COOL, with water at a ratio not exceeding 60:40 (60-percent antifreeze or coolant to 40-percent water). Mixing a long-life factory antifreeze product like DEX-COOL with water does not take away from its efficacy and may actually help it last longer. However, combining DEX-COOL with other coolant or antifreeze products can diminish its potency.

Step 6

Make absolutely certain that both your car's engine and coolant system are completely cool before you begin to work with them. When you have drained your car's coolant system and achieved the proper mixture of antifreeze or coolant and water, refill your car's coolant system with the appropriate solution and hit the road.

Learn more about coolant on the Road & Travel Magazine website (see Resources below).


  • While a long-life factory antifreeze product will have a life of 5 years or 150,000 miles, you will shorten this lifespan if you mix it with other coolant products. Many people simply mix ethylene-glycol coolant with their existing antifreeze because they don't realize they're actually compromising the overall efficacy of their coolant.
  • It is best not to mix different types of coolant or antifreeze with one another, unless it is unavoidable. A much better solution is to drain your car's coolant system and refill it with a single coolant-and-water mixture.
  • Use softened water whenever possible. Hard water can affect the chemical makeup of some coolant products.

Items you will need

  • Automobile owner's manual

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