I've heard from some people that they use straight antifreeze in their cooling systems, not 50/50.

  • What are the pros and cons of doing that?
    • E.g., does it reduce exposure to corrosion?
  • As an interesting note, there is a new product out called Evans Waterless Coolant. As the name implies, it doesn't require water. To use, you have to completely empty water based coolant, flush it with their special flush which removes nearly all traces of water, then put their coolant in. After it's done correctly, you never have to change the coolant again. Protection is from -40F to over +375F. Since there is no water, no worries from: overheating, pressure, corrosion, erosion. It's also completely reusable. Promises to be good stuff. May 29, 2015 at 10:44
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    Pure ethylene glycol freezes at about + 5 F. So if you live where it doesn't get that cold , it is alright to use. Jan 18, 2018 at 17:07

7 Answers 7


As explained on this page, using pure antifreeze alone will not do the job:

No matter which type or color your antifreeze is, it will transfer heat away most efficiently when blended with the proper amount of water - a mixture percentage based on the lowest temperatures typically seen in your climate. Most regions are best suited to a 50/50 water-antifreeze mixture which will provide protection from a low of -34°F to a high of 265°F. In addition, maintaining proper freeze point protection ensures corrosion inhibitors remain at intended levels.

It's interesting to note that pure antifreeze alone will not perform the task of protecting your vehicle's cooling system much better than water would by itself. In fact, pure antifreeze will freeze at a temperature not much below where water does. In the coldest climates, the most effective mixture against freeze-up will consist of 60-70% antifreeze (with the rest being water) - not 100%.


Using straight anti-freeze would probably reduce corrosion due it's lack of an oxygen that could be broken off from one of it's 'strings'. Adding water may dilute the anti-freeze but it makes it denser. The water also has that pesky oxygen atom that can be broken off from it that can cause corrosion. That being said, running straight anti-freeze in very hot climates increases the risk of heat related damage to the motor as the fluid will not as efficiently rid the system of heat.

Anti-freeze is made of ethylene glycol or propylene glycol. Both of those compounds are polymer strings that are pretty large molecules.

Water fits in between those molecules and increases the density of the anti-freeze. When the density is higher it will have more surface area against the channels, water jackets, etc. within the motor.

With a larger surface footprint it can then have a more efficient heat transfer mechanism. Adding water increases the heat transfer coefficient. Simply put it makes convection better.

Side note:

  1. It's similar to adding salt to water to increase the density of the water. We used to add salt to our cooler with bear and ice in them back in the day to shorten the time it takes to cool the beer. Try it with anything, you make things noticeably much faster with this trick.

  2. ethylene glycol or propylene glycol are both alcohol based thereby being water soluble.

If your into it, this is a pretty cool physics website.

  • Very good explanation of the why. Thanks for the education, Ducati. May 29, 2015 at 10:33
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    A bit late, but... 1) Heat transfer from the metal into the liquid is not the problem - it's more a matter of heat capacity, i.e. how much the liquid heats up when taking a given amount of heat energy. 2) Salt in cool water doesn't cool your much faster than the water itself. But add 33g salt to 100g of ice, and the ice cools down from 0°C to -21°C (32°F to 6°F) immediately, and the bears go into hibernation ;-) That's not a general rule: Use sodium hydroxide instead, and the water heats up to its to boiling point...
    – sweber
    Oct 29, 2016 at 11:57

Run your car without the radiator cap , with 100% antifreeze and you will find it doesn't boil out. Run 50/50 and it will boil out. My 1991 ford van has had 100% antifreeze in it for a number if years. The system is not pressurized and not one time has it over heated or froze. I use it for camping and at times in the middle of summer , we idle with ac on for hours , and idle to keep warm in winter. My 2001 olds aurora has a blown head gasket , remove its ability to pressurize , 100% antifreeze and wah lah , no over heating. Have driven it over 50,000 miles this way.

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    Welcome to the site? Nice anecdote, but I'm not sure how this answers the question? Please take the Tour and read articles in the Help Center to better understand how we work here at Stack Exchange. Mar 25, 2017 at 12:51

It's a horrible idea because:

  • The ideal coolant for an automobile is water. It has very high specific heat and is commonly available and cheap. The only reason we use anti-freeze is because water freezes at 0C and boils at 100C, which is not wide enough for the expected operating conditions of cars. The boiling issue can be resolved by running the system at a higher pressure or with a lower temperature thermostat, but freezing protection requires additives.
  • Paradoxically, pure ethylene glycol has a much higher freezing point than a mixture of water and EG. This actually negates the one benefit of putting EG anywhere near your car.
  • ethylene glycol has half the specific heat of water, so you'd be halving the energy transport capability of your car's cooling system. Possibly causing it to run hot depending upon prevailing conditions, the surface area of your car's engine and radiator, the thermostat temperature and the rate of flow of your water pump.

You should run between 100% and 40% water. The amount you should run depends entirely upon the likelihood of encountering cold weather. If it's always 100F where you are (day and night), you should run only water (with water wetter).

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    What would be the effects of pure ethylene glycol freezing in the engine? Water freezing causes immediate severe damage because water expands when it freezes, but from what I understand it's almost unique in that behavior. I would expect that attempting to run an engine for very long at any significant amount of power when coolant can't flow would be bad, but would there be any damage if the engine was thawed enough to allow fluid to flow before it was started, and it was then idled to warm it up gradually?
    – supercat
    Feb 21, 2021 at 18:55

I have been using straight antifreeze for the last 10 years. I stay cool, and I am no longer replacing hoses, water pumps, the radiator stays clean so I don't have to flush.I test it every year and it tests minus 40. I couldn't be happier.

  • when you say it "tests" -40 that is presumably a specific gravity test. Pure ethylene glycol actually freezes at -13c. Although it doesn't expand and crack you block like water I cant imagine your water pump would like trying to pump a solid.
    – agentp
    Aug 22, 2017 at 2:33

I ran straight green antifreeze for 23 years in a 79 Toyota supra after draining out the purple stuff that was in it.I never had a problem, no change in temp [it had a gauge] & when I would change a thermostat, the one I took out looked new! being a mechanic all my life I knew an aluminum head & cast iron block you could have electroless problem with dissimilar metals [corrosion].I've had An 80 Malibu cp. with an 454 with aluminum head and ran straight green antifreeze & it ran hot so I tried 50-50 mix no difference still ran same temp. back to straight green. The clutch fan failed and tep went to 275 And I heard a bubbling sound & figured I had killed it, I started it & slowly cooled it down with a garden hose no damage. I believe the boiling point is about 268 so it saved my engine.Jim


Pick an answer : Pure ethylene glycol freezes at about + 5 F ; the commercial product has a few percent water to lower the freeze point to about 0 F. The eutectic ( lowest freezing point) is about - 65 F with 50% water. It also has a higher boiling point than straight water. Many products sold today as "antifreeze" are actually a 50/50 mix , I expect this is what most people have that they call "pure antifreeze".

  • After 40 years I misremembered some ; glycol freezes at + 9 F .. The eutectic is 66% glycol at - 62F. Sep 29, 2017 at 15:57

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