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.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
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

I have wondered about this for sometime. My 92 has it, my 86 does not have the washer fluid loop. My '92 runs hotter.

Do you think it is related to capacity of the cooling system? You must have added some by reinstalling this system.

__________________
David
1986 300E Anthracite + ECodes + MB Mileage Award

Check your thermostat and replace it if you haven't done so in awhile.

The low temperatures could indicate a faltering thermostat and you don't want it to break in the closed position as mine did.

It was only in hindsight that I connected the cool running engine to the failing thermostat.

glenmore
1991 300CE
1990 LS400

Hi,
My '93 300e has that option; I thought the hot water loop into the windshield washer fluid was to prevent freezing in winter.
The alcohol mix in w/washer solution will evaporate out quickly at lelvated temps. Min does not normally get hot in the fluid in summer temps.

Al

The cooling capacity increased by one gallon, the size of the washer fluid reservoir. (As I use the washers, and deplete the fluid supply, my cooling capacity should diminish a bit -- at least until I refill the tank.)

My thermostat is Ok -- was replaced a few years ago after it went bad. At that time, the coolant temperature was about 60 on the highway (in late fall).

Today, the outside temperature dropped from the 90's to about 70, and the car running at 79 degrees at 50-60 mph (~2300-2800 rpm.) Time to increase my antifreeze ratgio a bit, just to keep the engine warm enough. In summer.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
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