This past weekend, I repaired my bypassed washer fluid heater coil after the thermo valve broke more than a year ago. Actually, I did not repair it, but simply replaced the lower brass piece that seals the thermo valve, with a bit of epoxy adhesive, and left out the upper brass piece and the spring. Coolant is now flowing freely, and rapidly, through the coil.

Since then, I have observed coolant temperatures of a steady 80 degrees at moderate speeds (40-60 mph) and 78 to 79 degrees on the highway (70 to 80-mph) – in 90 degree weather!

It seems incredible to me that an extra gallon of water (I am sure most of the alcohol/glycol has boiled out of the washer fluid) and the volume of coolant flowing through that coil, can have such a profound affect on overall temperatures.

I should add that my antifreeze to water ratio is abnormally low – 5% antifreeze – which is undoubtedly a big contributor to this. However, before reattaching the heater coil, I was not dipping into that temperature range.

Has anyone else ever experienced this? Seems like a potentially effective way to drop a few degrees from chronically hot-running cars.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black