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Water vs Coolant on race engines

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So on the youtube live of engine design, someone asked why water over coolant, mentioned papadakis saying water over coolant and some other name i didnt catch...

Ive been told not to use coolant due to it being very slippy on the track if it ever leaks onto it, but i saw answers contrary to using water over coolant....

Whats the real deal? Water or coolant? Benefits? Regulations? This got me thinking, hopefully ill get some experienced insight.

There're going to be a LOT of differing opinions on this, and here's my 2 cents' worth.

As you say, sometimes you don't have a choice and have to use water - hopefully with a anti-corrosive and/or water wetter added. Water is a 'coolant' but I'll generally use 'coolants' as referring to either a pure replacement of a mix with water, eg, anti-freeze.

For the 'best' cooling, water is still the best as it has the best thermal heat capacity at 4200joules/kg/C - that means it takes 4200 joules of energy to raise 1kg of water by 1 degree centigrade. Coolants take less energy to raise their temperature and, as you may surmise, to keep the engine at the same temperature you will need to pass more coolant through it or, for the same amount of coolant, have the engine run at a higher temperature.

The biggest problem with using just water (and a wetter/anti-corrosion additive) is it is temperature limited - it freezes below 0C which can be a problem in cooler climes, and it boils at 100C at sea level pressure. I emphasis the 'sea level pressure' as it lowers with lower pressure (this may be significant at, say Pikes Peak altitudes) but increases with pressure* - that is why a pressurised cooling system is used with a suitably rated 'radiator' cap, that can raise the boiling point substantially - eg, 20PSI (guage, 34.7 absolute) brings it to ~126C. That's great until you get a leak that bleeds the pressure off ;-) - IIRC, F1 engines are running around 4 bar of coolant pressure!

Coolants, as I mentioned earlier can't remove as much energy, as such, but they have the advantage of being liquid over a much greater operating range, with anti-freeze additives/pre-mixes not only lowering the freezing point but raising the boiling point. Personally, I run a 25-30% mix and it has allowed me to run into the red on occasion - NOT something recommended, but... On anti-freeze blends and pre-mixes, back in the day they were basically fill and forget, but with environmental controls there are now a LOT of variations and they have different service lifes between replacment being required - I did get caught by this with 'old' anti-freeze, blowing a core plug in a head but, fortunately, with no other damage.

Another type of coolant is a direct replacement where ALL water is removed, such as https://www.evanscoolant.com/ and this has a big advantage in that, because there is no water, there is no possible cavitation in the water pump, which can otherwise do a lot of damage. Haven't used it, but hear good things about it - but it is probably illegal for some race series/tracks because it doesn't wash off as easily. If I were to build something nowadays, I would be seriously considering using it, if legal!

*you can play around with it here - https://www.omnicalculator.com/chemistry/Boliling-point - but note, that uses absolute pressure, so you need to add 14.7psi, or 1 bar, to guage/pressure cap to correct for it.