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Extending an exploration of windshield washer-fluid choices to freezing points of methanol-water mixes, all web-sources located agreed to within a couple of degrees from 0-60% w/w, yet above this proportion (and below 100%), repeatedly came across conflicting data (which fell into three groups). (Yes, the disagreements are all outside the range of winter driving on this planet - except perhaps for around Vostok Station...)

w/w various graphs by eye various tables engineering toolbox table all˚C
60% - 71 - 71 - 71 ˚C
70% -102 -137 - 82 ˚C
80% -116 -143 - 87 ˚C
90% -108 -146 - 90 ˚C
100% - 96 - 98 - 98 ˚C

examples of sources for above data:

http://www.methanol.org/wp-content/uploads/2016/06/FreezingPointsMethanol-WaterSolutions.pdf graph
https://patents.google.com/patent/WO2011153147A1/en table (~ 1/3 way into the document) https://www.engineeringtoolbox.com/methanol-water-d_987.html table

Thanks for any comment.

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    $\begingroup$ Different source data, different data processing, different errors made. $\endgroup$ – Poutnik May 5 at 7:07
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    $\begingroup$ Thanks. Your emphasis on "different" inspired a new search strategy which led to a satisfactory answer to the question. $\endgroup$ – revans19 May 6 at 6:43
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From Solid-Liquid Phase Diagram of the System Methanol-Water by G. A. Miller and D. K. Carpenter in J. Chem. Eng. Data 1964, 9, 3, 371–373 (July 1, 1964) [https://doi.org/10.1021/je60022a017]

"A solution of methanol and water that is methanol-rich tends to form a glass when cooled below the melting point. The liquid is very viscous at such temperatures (below -100° C.) because of the presence of hydrogen-bonded polymers. Because it is difficult to induce crystallization, the melting point is determined from a warming curve. Much of the wide divergence of melting point data for the composition range of 55 to 95 mole per cent* methanol results from the use of cooling curves."

* by a back-of-a-napkin calculation (assuming 32.042 g/mol MeOH and 18.015 g/mol H2O) the mole percentage mentioned is approximately 68% to 97% methanol (w/w).

Further - successful - online research was inspired by a comment; it appears the failure to find information with common search terms was due to a language difference. It seems specialists (presumably physical chemists) use "solid-liquid equilibrium" or "solid-liquid phase diagram" in documents which may completely exclude the term "freezing-point" - such as the publication quoted above which answers the original question.

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