Ran across this on a motorcycle forum I frequent. Have no idea if it applies to a coach, but will check. Comments?
https://www.hemmings.com/stories/cold-and-shocking-have-you-checked-the-voltage-of-your-coolant/
Yes and if doesn't it wouldn't hurt to check. Antifreeze at the end of its life without being supplemented will start producing electrolyses and is being reactive and corroding. Past the end of life much damage can occur pretty quickly. This is intensified if the system has steel, aluminum, and brass. Well worth checking. Same principle as the anode in a steel hot water heater.
The writeup says to NOT use distilled water, and better to use soft water. This is contrary to what many have done. Also mentions radiator core metal compositions.
A little research takes me both ways.
One interesting recommendation is to use rain water.
That one would be tough here in San Antonio.
Ah, but what we run in our cooling systems isn't distilled water. It's coolant, of which water is the solvent. Other than a flush (which still won't be 100% distilled water; just highly diluted coolant and then only for a brief time), the system isn't in contact with nothing but water.
Modern coolants include corrosion inhibitors and other additives formulated to protect the system.
I would be more concerned about the pH of soft water potentially mucking up the coolant chemistry. Soft water tends to be slightly acidic, where distilled is pH neutral.
Equally important consideration is total dissolved solids. These are mostly minerals and salts and I don't want that in my coolant system. Most tap water is pretty high in TDS and mine is close to 500ppm. TDS can only be lowered by reverse osmosis or distillation. The distilled water I bought for my coolant change measured 0ppm. The R.O. water i used for flushing the system measured around 10ppm. I also used Cummins Restore cooling system cleaner. If one is concerned about the aggressiveness of the water they use it is possible to blend distilled or R.O. water with tap water to acheive any level of contaminant they prefer. I did not check ph of my water because I assumed that it would be in an acceptable range.
Jogged my memory that Steve had our tap water tested since he's a homebrewer. Turned out we have "darned-near-distilled" tap water. He has to add minerals back in for brewing or things don't ferment as well.
pH 6.9
Total Dissolved Solids (TDS) Est, ppm 17
Electrical Conductivity, mmho/cm 0.03
Cations / Anions, me/L 0.3 / 0.2
ppm
Sodium, Na 5
Potassium, K < 1
Calcium, Ca 1.4
Magnesium, Mg < 1
Total Hardness, CaCO3 3
Nitrate, NO3-N < 0.1 (SAFE)
Sulfate, SO4-S < 1
Chloride, Cl 3
Carbonate, CO3 < 1.0
Bicarbonate, HCO3 5
Total Alkalinity, CaCO3 4
Total Phosphorus, P 0.17
Total Iron, Fe < 0.01
"<" - Not Detected / Below Detection Limit