I just replaced my radiator today and decided to refill it with coolant concentrate and mix in water myself. Instead of mixing the stuff properly before hand, I poured in 1/2 gal. of water directly into the radiator, and then proceeded to pour in 1/2 gal of coolant in and it filled up only after pouring in 1/4 gal.

Q. Do I have to mix the coolant beforehand or can I count on it mixing in the radiator? Also, will my pipes freeze/crack overnight (it's 29° f tonight) if there is like 60% water and 40% coolant?

  • 1
    you are fine, it will mix and 40/60 is good to at least 0F
    – agentp
    Commented Feb 7, 2018 at 4:01
  • @agentp thanks! Should I even bother refilling it with 50/50 when the weather gets warmer or can I leave it? Just wondering if any type of performance will be affected... Thanks!
    – harvey
    Commented Feb 7, 2018 at 4:23
  • Check the label; many marketers sell premixed 50 : 50 but it is not clearly marked and may be mistaken undiluted antifreeze. Commented Feb 8, 2018 at 1:26

2 Answers 2


I'd need the vehicle year and model to know the exact total system capacity, but I'm guesstimating that's somewhere around 3-5 gallons.

You have added 3 quarts at a non-ideal "top-off" of 66% water and 33% coolant.

Assuming the worst case (your total capacity is only a few gallons) your overall coolant ratio is still probably fine to far below your expected temperatures.

Now if this a Mahindra Exedar 333 Elite you plan to ship to the Columbian Ice Fields (specifically, the 820cc diesel hybrid), I would consider draining a bit and adding more unmixed glycol.

That's a joke; you're fine.

As an important aside, "wind chill" does not affect vehicles. I had a long argument with an "adult beverage patron", which I ultimately lost, due to my own folly in engaging in the first place. As my mother was fond of saying, "Never try and teach a pig to sing. You get nowhere and it annoys the pig."

  • Thanks! It's a 2007 Nissan Maxima. I think total capacity is around 2 gallons, but I could be way off.
    – harvey
    Commented Feb 7, 2018 at 4:29
  • @harvey you are pretty close, my sources whisper 2.25 US gallons for the 3.5 liter. (Great engine, BTW). You're fine.
    – SteveRacer
    Commented Feb 7, 2018 at 4:48
  • thanks for the confirmation! Love the 3.5 but it's a guzzler (13mpg avg.)
    – harvey
    Commented Feb 7, 2018 at 4:49
  • @harvey, true, sure, but the ... the ... grunt de los heuvos in such an otherwise innocuous vehicle...
    – SteveRacer
    Commented Feb 7, 2018 at 5:04
  • All I can say is "poor pig" ... although, they can suffer from wind chill :o) Commented Feb 7, 2018 at 13:46

The engine will blend the water and concentrate mixture, once it's started. Typically you should start the engine after you poured the fluids in. Whenever you replace the coolant certain amount of air remains trapped in the loop. After an initial filling, starting the engine helps to bleed out that air. The air comes out from the radiator cap. You will observe that the coolant level has gone down after the initial start.... Top it up and run the engine again until there is no air left in the system. A few sharp revs help bleed the air out fast. Your system is completely filled when coolant is up till the brim of the radiator cap.

About the mixture : A 50/50 blend is preferable but it varies for different coolant manufacturers. Check the lable, the coolant has a temperature rating for it's mentioned blend.

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