I decided to flush my radiator and fill it with fresh anti-freeze before the really cold weather hits. Get to the local Auto Zone and I see anti-freeze on sale for $8.99/gal. But wait, it’s Prestone 50/50, 50% anti-freeze/50% water.
The regular Prestone is $9.99/gal. Let me think for a sec… $1 more for twice as much and all I have to do is add my own water. OK, I’m sold.
That’s a heck of a racket, but I bet they sell a lot of it.
Have you ever figured the price per gallon of the bottled water you buy at the local convenience store? That Prestone water is a bargain.
There’s a thought: Top off the radiator with Evian. 
FWIW, I don’t drink bottled water. I’m not going to pay that much for water to go into me, much less my radiator.
Something is telling me the price of the water in that 50-50 Prestone is higher than $4.50 a gallon, but it still feels like Monday morning to me and I don’t feel like doing a high school algebra question.
And I have bought the 50-50 before, while I was on a road trip and found that my collant was low for some reason. It just seemed so much easier to buy that stuff and not try to mess with finding water, mixing it in approx. the correct ratio, and so on. You see, I make a nice living, and wasting a couple bucks not to bother with the (admittedly minor) hassle can seem like a good investment.
It’s $8/gal, ignoring the 1c here and there. If a gallon of antifreeze is worth $10, then the half gallon in the mixed bottle is worth $5. The listed price is $9, so there’s $4 worth of water in there. But that’s only half a gallon of water you get for that price. The whole gallon of Prestone water would be $8.
Harrumph! Only the finest of bottled water should go into one’s radiator - Ozarka Natural Spring Water .
I like to keep my car happy and content, (and it’s only a buck or so a gallon). 
Do not follow my advice as I’m just crazy like that.
Use distilled water. It keeps the crud from forming in your coolant system.
You always pay for convenience. Like the little plastic packets of oh-so-super-special dishwashing liquid? If you get, say, 20 in a box for $5 but a bottle of the liquid washes 30 loads it might only be $4. And then sometimes if you get the box of the powder it washes 40 loads for $4. Ridiculous, but it works because people pay for it. Either they figure the convenience is worth it or they fall into the marketing ploys of catching your eye so you say “Ooooh, new and shiny!” and then buy it without considering the price tag. (Something we are all guilty of…)
To be absolutely precise, it’s $7.99 per gallon. But for comparison shopping with bottles of Evian, $8 would be close enough.
The 50/50 was $8.99/gal, so I rounded to $9.
50% of $9 is $4.50, that’s where I got the cost of 1/2 gallon of water.
I knew when I posted that figure that there would be discussion of the $9.99 I paid for the gallon of 100% anti-freeze, or some rounding error or something.
If I have $9 and you ask for 50% of it, I’d still give you $4.50. Then you could buy Evian, or pay somebody to mix the Prestone with Perrier for all I care
And I now see my math error. It was $4.50 for 1/2 gallon, so the Prestone water was the same cost per gallon as the 50/50 mix or $9 ($8.99)/gal.
No wonder I don’t make enough to have my anti-freeze pre-mixed :smack:
This kind of thing is why I tell my students to buy a half gallon of ammonia at the 99 cent store and skip buying Windex.
Just a dumb question; using water as a coolant causes all kinds of problems, including:
-corrosion of the engine block
-deterioration of the water pump
-deterioration of the head gasket
face, H2O is very corrosive. Why noy use a light oil as the coolant? The dvantages;
-no corrosion
-no water pump lubrication problesm
-no need to change the "antifreeze)
I know, the heat capacity of H2o is enormous-but just use a larger radiator. Would cooling the engine with a light oil make sense?
a. Water is cheap and readily available.
b. Oil is messy. The consequences of a boil over or radiator leak would be really nasty and hard to clean up.
c. Water, as you pointed out, has some nice thermal properties.