[alfa] Re: Homemade windshield washer fluid?

[Sonny <maxid@xxxxxxxxxxxxxx>]

Thanks to those who replied on and off digest. Since some requested that I share information, I will bring on a few tidbits that I found on the Web and on amazon.com, using their new search feature.

Windshield fluid for cold climates uses Methanol, ethylene glycol, or propylene glycol as a deicer. Methanol is also a good glass cleaner, so it is universally used. Pure methanol freezes at -97.8 C (-144 F). However, you can't use more than a 33-40% (depending who you ask) solution because flammability becomes a problem.

For added protection, one can add ethylene glycol or propylene glycol. Both are also used as antifreeze in engine coolants. It is commonly known that these coolants, as opposed to methanol, are less effective undiluted than in a solution with water. The eutectic solution for both of these glycols is around 63%. Their eutectic temperatures are very low, -50 to -70 C, but in practice it is not feasible to guarantee protection to these temperatures because the freezing point increases steeply at either side of the eutectic concentration, so the properties of the fluid are difficult to control (the reason we never use more than a 50/50 mix for engine cooling seems to be the price paid in terms of heat transfer at operating temperature). 

Propylene glycol is more expensive than ethylene glycol and more viscous at low temperatures, but has less of an impact on the environment. 

Thus, one could use a 30-40% methanol mixture with some ethylene or propylene glycol thrown in. However, without additional information it is impossible to predict the freezing point of a given water/methanol/ethylene glycol mixture. This is exactly what for instance the PEAK -30 brand does. The propylene glycol content is less than 5%. Why it is so low is anybody's guess, but it could be due to viscosity problems at low temperatures or environmental concerns. Speaking of environmental rules, methanol also seems to be regulated by VOC (volatile organic compound) rules in California and elsewhere. 

I think the easiest solution is to try the PEAK brand or one of those products recommended to me by other digesters next time. 

On a related note, I have sometimes gotten gray streaks from the washer fluids on the windscreen. It doesn't seem to happen now, and I am running a fluid which seems to be methanol/water, no glycols. Could it be that it is glycols that is responsible for the gray streaks I used to get?

Sonny
'91 164 S
Baltimore
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided