A lot of these w-w fluids are at least partially methanol. As such, you should not get the un-diluted fluid too hot as it could boil. Used to use a 50/50 blend of water and MeOH as antifreeze and it would boil out in early spring. Otherwise made a good base antifreeze.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Soak a 100 dollar bill in that mixture (50/50) then set it on fire.

People won't belive you just lit it up until they see how the dollar looks when the flames go out.

Had a lab TA mess that up once...they mixed up some 90/10 somehow instead of 60/40. The dollar bill went up in flames hahah.

I think if you're going to wait for the engine to get warm before you use your washer, you could be running the defrost to warm the windshield as well. The in-line electric heater seems a better solution.

The only time you would need it is when it is bitterly cold outside, and your car isn't warm yet. In the past 10 years, I have had the washer fluid freeze up on my windshield maybe 3 times. I wouldn't deem it as absolutely necessary myself. Besides, aren't there chemicals in washer fluid that keeps it liquid unless it is really cold?

The only time I ever have washer fluid freeze on my windscreen is when it's 5* or lower with a good wind.

Most car stores sell the purple washer fluid that's good down to -34*f. then there is always the ice-melting additives.

EDIT: Sweet! This is my 2500th post!

Methanol boils at about 148F. The coolant heated line would boil it away. Not a good idea. However, if you can limit it to 120F or so you would be fine. I have some left over heater wire that would do the trick...

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.