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I design and manufacture high performance radiators. I recommend 50/50 regardless of climate. As has been pointed out, there are many factors you need to evaluate when designing a coolant. These include latent heat, density, viscosity, lubricity, surface tension, boiling point, and oh yeah, specific heat. I just want to point out some misconceptions that have been voiced here, elsewhere, all over the web, with regard to specific heat.
First, let's take another look at the chart that TJTS put up. I've attached an annotated version. The first question you should ask is what are the conditions of measurement? If specific heat is represented as a single number, it only has validity for one temperature and pressure. Specific heat isn't a point, it's a curve. For water, it doesn't matter much because it's always going to be close to 1. But glycol's specific heat increases significantly with increasing temperature. So while it may be .59 at room temperature, by the time you get to 212F, it's around .69.
The next question is what units are you looking at? Take a careful look at the chart: the dimension is BTU/lb/degreeF. The importance of this is that you're seeing a number that's reflects weight, not volume. You don't fill your radiator with 16lbs of coolant, you fill it with two gallons. Glycol is 12% heavier than water, so if you fill your radiator with it, you have more coolant by weight, and 12% more thermal mass is an important difference.
When you add it up, at higher temperatures a 50/50 mix will have about 90% of water's heat transfer capacity, and pure glycol about 80%. And that's without taking into account that glycol mixes can run much hotter than water. Not what you would expect from a casual glance at TJTS's chart. So you're not giving up much with 50/50. And you get more than a few benefits:
- Higher boiling point. Overheating is boil over, not just running hot. A glycol mix can raise boiling point by up to 20f.
- Less likelihood of cavitation in low pressure areas due to lower vapor pressure and lower surface tension. If you look at the pump involute of a car that's been running pure water, it usually has pockmarks. This isn't ordinary corrosion, it's metal blasted away by localized boiling.
- Pump lubrication
- Corrosion protection
- Freeze protection
- Viscosity compatible with system design
- Consistent with manufacturer's warranty if applicable.
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