After doing my 3K oil change today, I siphoned off everything from the upper tank, a tad more than 1/2 gallon. Topped off with bottled water and a refresher of about 3 ounces of water wetter.
While the engine idled, circulating the new oil, I placed a thermometer in the upper tank and compared the thermometer to the temp gauge for accuracy. When the temp gauge showed a little over 175F the T-stat opened, and the thermometer rose. Finally stabilized ~190F ( with the gauge showing about 1/16 of an inch below the hash mark between 175 and max).
I'm going to watch it close for a few days, see what happens with the mix watered down a little. I'll get a highway run in, with a few grades, and see how it looks.
I did notice that the coolant I removed (with the water wetter in it) was very, very slick, most likely the slipperest water I've ever felt. I guess that's the extra lubricity of WW.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.