alt Hacker NewsIs it specific heat that we care about, or rate of heat transfer? Specific heat matters a bit, but if you make your coolant take twice the energy to change 1 degree, the same thing happens on the radiator side and you must release twice the heat to cool 1 degree.
Rate of heat transfer in general if probably more important.
Well, it gets really complex. Yes, specific heat matters, but as you say so does the heat transfer coefficient. And the viscosity. And is the flow laminar or turbulent? Etc.
There are various figures of merit, such as the Mouromtseff number https://doi.org/10.1109/JRPROC.1942.234654 or https://www.electronics-cooling.com/2006/05/comparing-heat-t... for a quick overview.
Some tables of heat transfer coefficients: https://www.engineersedge.com/heat_transfer/convective_heat_...
But, turns out water is just very very good also when you take these other factors into account. Compared to oil, it has, as mentioned, much higher specific heat, it has higher heat conductivity, it has lower viscosity which means less pumping power and more likely to see turbulent flow which helps with mixing.