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why mix coolant 50/50?

06-29-2004, 08:46 PM
This is something I have never understood. Why do people mix collant 50/50? When I lived in the upper penninsula, I talked to a shop tech and he said not to mix it 50/50 because it got so cold up there that a 50/50 mix could freeze. He recommended pouring it straight in without mixing it. Some cans of coolant I've seen have charts on it saying that 50/50 protects to a certain temp and 60/40 is a little colder, 70/30 is even colder, etc. And the only reason I can think of why people mix it is to save money. But why mix it to save $2 and risk ruining your engine (for $2!!!)? It makes no sense to save $2 in coolant, but in return have to replace your engine because it overheated. But my dad insists that mixing it makes the coolant protect against colder temperatures and the tech that told me otherwise (and all the labels that has the charts) are wrong. So can somebody explain this to me!!



06-30-2004, 05:33 AM
Water is added to the coolant to ensure that the coolant can provide maximum protection at a wide range of temperatures. 50/50 seems to be the standard mix, but you can change it slightly depending on the environment you drive your car in.

I would believe that your dad is right (according to everything I've read).


06-30-2004, 02:06 PM
Water is a much better coolant than antifreeze because it is able to "absorb" more heat energy than ethylene glycol (and other antifreeze ingredients) and carry it to the radiator for disipation into the air. In physics, this is referred to as the "specific heat" of a substance and refers to how much energy (joules) it takes to raise the temperature of one gram of that substance by 1 degree celcius. It takes 4.2 joules for water, 2.2 for ethylene glycol and 1 joule for air. Or in other words, you can pump more energy (heat) into water with less increase in its temperature as compared to ethylene glycol. Therefore about twice as much fluid would have to travel through the engine to remove the same amount of heat energy when comparing water to ethylene glycol, assuming you wanted to keep the engine temp constant. The low specific heat of air is why we have to have so much surface area on a radiator to take the heat energy out of the fluid. Of course, water alone provides no protection for corrosion and will freeze, thus antifreeze coolants were invented. Based on what environment you drive your car, you pick the mix that is best suited to protecting your engine and coolant system from overheating, freezing, and corrosion. Ethylene glycol also weighs less per gallon than water, which requires more volume of fluid since specific heat is measured per unit of weight, not volume. While ethylene glycol in general is worse for heat dissipation from the engine, it does have one positive contribution in that it will raise the boiling point of water keeping a borderline overheat situation from turning into a boilover.

07-02-2004, 08:38 PM
Yay for hydrogen bonding!

07-06-2004, 07:27 PM
Thanks for the refresher course in heat transfer, thermodynamics, and chemistry. I had forgotten most of the details!

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