hellafunctional Rotating Header Image

Things you should know about coolant

This will be the first winter my car will spend in a cold climate in a few years, and I realized that my cooling system is in danger of freezing if I don’t add some anti-freeze. This brought me to look up the ideal water to coolant for cold weather usage, and then lead to much more research on cooling systems and how coolant works. I thought it might be a good idea to share results on how the boiling point, freezing point, and heat transfer ability of coolant change depending on the mixture. Also, this would have been easier if my thermodynamics textbook wasn’t in a storage unit 1000 miles away.

Anyhow, because the whole point was to look up freezing points I’ll start there. The freezing point of water as we all know is 0C (32F). You might presume that the freezing point of ethylene glycol, the main ingredient in most automotive coolants, is very low, and that a system filled with only anti-freeze would be the ideal choice for cold winters in places like Alaska and North dakota and Canada. In reality, it is only -13C (8F). That’s not very cold! If you were to only use coolant in a cold climate, the possibility of it freezing is very possible (although it’s not water and would not expand as such, so damage to the engine block and cooling system would not be a worry). The key is the mixture of coolant and water. When done in the proper proportions, the freezing point gets much lower:

From that you can see that the ideal mixture for extreme cold weather is about 65% anti-freeze and 35% distilled water. Now, unless you live in a very cold climate, you might be concerned with what happens when the coolant is hot. Anti-freeze alone has a pretty high boiling point of 197C (387F), which is much higher than you would see in an automotive cooling system. Water, of course, boils at 100C (212F). When mixed. we end up somewhere in the middle:

The interesting thing here is that it takes quite a bit of anti-freeze to get the overall boiling point of the coolant to increase by a significant amount. Much like the freezing point, a 50/50 mix doesn’t split the difference, and at that ideal mixture for cold of 65%, we’ve only increased the boiling point by about 15C (27F).

When it’s hot out and the car is under a lot of load (say going up a hill in the desert or doing laps around a race track), it’s important to keep the coolant from boiling, because boiling coolant doesn’t do it’s job very well. Most engines operate at around 90-105C (190-220F), which is very close to the boiling point of this water/coolant mix. Thankfully, there is something else that can be done besides varying the mix- increase the pressure. A standard cooling system operates at about 15psi, which if filled with straight water would boil at around 121C (250F). This is above the normal operating temperature of an engine so there actually isn’t much reason to worry about the composition of our coolant in a pressurized system.

When we’re on the hot end of the temperature range, the much more important value in the cooling system is what’s called the specific heat capacity. The heat capacity is basically how much heat energy the coolant can carry out of the engine and to the radiator. As far as carrying heat goes, water does a really good job. It’s actually one of the most effective coolants that could possibly be used. The specific heat capacity of ethylene glycol is only about 65% of water at the temperatures seen in a cooling system. That means that to cool the engine by one degree, you would need about 50% more of it than straight water. So even though you could use pure antifreeze as a coolant, or any other liquid for that matter, you would need a bigger radiator and more robust cooling system compared to one that used straight water. Here is what happens to heat capacity as our coolant mixture changes:

From a cooling point of view, it seems ideal to have the system filled 100% with water. At that 65% mixture we’ve lost 20% of the cooling capacity of the system, and when the cooling system is being used at near capacity, such as on a race track, canyon drive, or simply a hot day with the a/c on, it could mean the difference between a fun time and being parked on the side of the road with blown headgaskets.

While pure water has the highest possible heat capacity, it’s not quite the ideal automotive coolant. Aside from freezing, water can also corrode the inside of engine blocks, radiators, and water pumps. We need to have something in there to keep iron blocks from rusting up and water pump bearings and seals from failing. Anti-freeze contains these necessary additives and most auto manufacturers have pretty specific requirements on the types of coolant you can use. So, for the most part it’s a good idea to put some of the recommended coolant into the system, however, if done at a lower ratio, the cooling capabilities of the car will improve. If you live in a warm climate, it’s not a bad idea to drop the coolant: water ratio down to 25 or so percent to gain cooling capacity without loosing the anti-corrosion and lubrication properties (although it will be necessary to change the coolant more often if you do this because anti-freeze degrades over time).

There are also additives on the market specifically meant for systems that run 100% water, like redline’s water wetter and motul mocool. These products also claim to improve the cooling capacity of straight water to reduce running temps. This is because there’s more to cooling than just the heat capacity of the coolant. What occurs on the boundary between engine parts and the coolant is also important. This is where the additives come it: they reduce the surface tension and “wetting” capacity of the water, which will make a slight improvement in how well heat can be transferred from the block to the water.

Most marketing and testing for these products compares a 50/50 water and ethylene glycol mix to pure water with the additive, and show dramatic reductions in coolant temperatures. Most of these gains actually come from the added water content, and not from a magical additive. However, there is still a benefit to use them because in addition to improving the heat transfer ability they have anti-corrosive and lubricating properties.

So, in conclusion, you should only use as much anti-freeze as is necessary for your climate and operating conditions, and those coolant “wetting” additives are generally a good thing to use.

Coming eventually- some tips on improving the cooling system to keep a track or modified car cool.

Don’t fill her up with antifreeze, Alaska Science Forum
Ethylene Glycol product guide (pdf)
CSU engine web page
Ethylene Glycol heat-transfer fluid
Increased cooling power with nucleate boiling flow in automotive engine applications


  1. [...] = 250; sr_ad_new_window = true; sr_adspace_type = "graphic"; Good discussion http://hellafunctional.com/?p=629 Also The pressure cap on a cooling system is the key to raising the boiling point of the 50/50 mix [...]

  2. [...] high in minerals tap water should be fine when mixed at the proper ratio with coolant. Now that ‘mixed with coolant’ part is essential. Some people insist on running straight water in their car’s engines (clearly they don’t live [...]

  3. [...] "How Car Cooling Systems Work" Antifreeze – Wikipedia, the free encyclopedia Things you should know about coolant – hellafunctional Antifreeze [...]

  4. [...] keep the metals from corroding. More than 65/35 and the freezing point actually gets warmer again. Things you should know about coolant – hellafunctional Either you bled some air out of the system, unclogged a blockage or are imagining your car is [...]

  5. Hariapte says:

    Thank you for the information. Good work.

  6. […] point. Fun fact: the freezing point of pure ethylene glycol is actually +9 F! Check this out: http://hellafunctional.com/?p=629 For spark plugs, get the Denso 3253. Another option is NGK 3452, but they are more expensive. You […]

  7. You have made some good points there. I looked on the internet
    for more information about the issue and found most people will
    go along with your views on this site.

  8. Demetrius says:

    Aw, this was a really nice post. Finding the time and actual effort to produce
    a top notch article… but what can I say…
    I hesitate a lot and don’t manage to get anything done.

    Feel free to visit my blog post :: insurance comparison;

  9. In order to work 50 weeks a year, you’re going to have to work
    30 weeks; in order to work 30 weeks, you’ll likely have to work 10.
    “Arsenio was a big hit way back when, he exited prematurely, and
    aren’t we all just plain tired with Jay Leno and Letterman.
    Do some research and find out as much as you can
    about each open mic – try to find the one that is
    most positively reviewed, gets the biggest crowd and that is attended by the most comedians.

  10. Don’t ignore it higher than the top to wet the ice
    cream. Empty the batter in to the cake pans and bakes for 35-40
    minutes or when a skewer is released clean. If a current customers are purchased, you may have
    beginning balances for a lot of GL sub-accounts.

  11. Calvin Klein says:

    I am curious to find out what blog system you are working with?
    I’m experiencing some small security problems with my latest website and I’d like to find something more safeguarded.
    Do you have any solutions?

  12. […] this page there's a chart of typical coolant effectiveness… http://hellafunctional.com/?p=629 __________________ KitaCamry: an 05 J-vin LE 2.4L/I4 manual tranny with 17" […]

  13. Fantastic beat ! I wish to apprentice while you amend your site, how could
    i subscribe for a blog site? The account helped
    me a acceptable deal. I had been a little bit acquainted of this your broadcast offered bright clear

  14. An interesting discussion is definitely worth comment.

    I do think that you ought to write more on this issue,
    it might not be a taboo matter but generally folks don’t talk about
    such subjects. To the next! Cheers!!

  15. Frederick says:

    EPA and DHA are precursors to eicosanoids that reduce inflammation throughout the body and scientists know that some sort of inflammation is behind just about
    every health problem we have. 256g or 256mg of omega-3 fatty acids and
    carries consumption advisories for children due to mercury content.
    So this means that you should be careful to make sure you consume enough Omega 3 because Omega 3 deficiency is responsible for many different health conditions.

  16. Thanks for sharing your info. I truly appreciate your efforts and I will
    be waiting for your further write ups thank you once again.

  17. Tremendous challenges the following. Now i’m able to view your publish. Thanks a great deal with this particular having a look in advance to call you actually. Can you remember to lower us a postal mail?

  18. […] and boiling points" got me this site which I haven't vetted but looks ok at first glance. http://hellafunctional.com/?p=629 1971 240z HLS3014364 joeytekno is online now   Quote Quick […]

  19. Webster says:

    What’s Going down i am new to this, I stumbled upon this I have
    discovered It positively helpful and it has helped me out loads.
    I’m hoping to contribute & aid other customers like its aided me.
    Good job.

    My homepage – Webster

  20. Hello i am kavin, its my first time to commenting anywhere, when i read this article i thought i could also make comment due to this good piece of writing.

  21. s110 canon says:

    Terrific work! That is the type of info that should be shared across the
    net. Shame on the search engines for no longer positioning this submit higher!
    Come on over and consult with my site . Thanks =)

  22. Hello There. I found your blog using msn. This is a really well
    written article. I will be sure to bookmark it
    and come back to read more of your useful information. Thanks for the post.
    I’ll certainly return.

  23. I just like the valuable information you supply on your articles.
    I’ll bookmark your blog and check again here regularly.
    I am moderately sure I’ll learn a lot of new stuff right right here!
    Best of luck for the next!

  24. Al-Shabab is fighting to create an Islamic state in Somalia. “Kenya has stared down evil and triumphed.” said Christian. cinematographers and crew who have been involved in and have continued to support Lucas and the franchise. He also made no apology for its past actions, who subsequently chose to bring her NLD party back into the political process, His background and commitment to Islamic values appealed to most of the devout Muslim Turks who were alienated by the state. while he was working for Istanbul’s transport authority.” Easy care Experts at the UN say simple and inexpensive care, A full term baby is when pregnancy lasts 40 weeks.

  25. Jorge says:

    My brother suggested I may like this web site. He used to be totally right.
    This post actually made my day. You can not believe simply how so much
    time I had spent for this information! Thank you!

    Visit my homepage: internet (Jorge)

  26. I’m gone to convey my little brother, that he should also go to see this blog on regular basis to obtain updated from latest gossip.

  27. Miami Heat says:

    Sesekali mulutnya bersiul kecil. Ambil gambar?saya takkan culik awak lagi?? Amna mengeluh. Setakat hari ini,pelupanya aku, Achik dah rasa, senak…. Ya Allah…. Membuat Khairul terfana. “Tidak!

  28. e3300eb16b6f8e5bae9c229bc9332b8b,Michael Kors

  29. Biasa la rumah orang bujang mana boleh bagi lelaki bukan muhrim masuk tak manis orang lihat.”ADLINA meneliti ikan selar kuning di hadapannya.” Adlina memeluk tubuh anaknya yang sedang menangis di bahu jalan perumahan itu.”Hello dikna,Bangdol tanya aku dengan soalan yang memalukan tu.”Bersih je tangan ni”.jgn pndang rndah ngan kitorang la.ROUZ! “okeyklu gitucg kne blnje kitorang mkn kat NZ CURRYtp dgr syarat cg amek kitorang 8 org kat umah masing2deal?aku cuba menolak walaupun ini merupakan peluang yang julung kali orang dapat. “Takde”, Setakat bersajak dengan buat novel je.

  30. First of all I want to say excellent blog! I had a quick question in which I’d like to ask if you do not mind.
    I was curious to know how you center yourself and clear your thoughts prior to writing.
    I have had a tough time clearing my thoughts in getting my ideas out.
    I do enjoy writing however it just seems like the first 10
    to 15 minutes are usually lost simply just trying to figure out
    how to begin. Any suggestions or hints? Cheers!

Leave a Reply