Coolant versus water — which cools your engine better?
When it comes to whether coolant or water conducts more heat, the answer is simple; water wins. But there’s way more to the issue than just heat transfer.
Coolant versus water when it comes to corrosion
Cooling systems contain many different metals; steel, aluminum, manganese, and copper. Any time you combine dissimilar metals with an electrolyte solution, you get galvanic corrosion; an elector-chemical process where a metal that’s more reactive than the others acts like an anode and another as a cathode, causing an electropotential difference.The electropotential difference causes the ion migration from anodic metal into the electrolyte and then to the cathodic metals.
When you use plain water as a coolant, the water becomes the electrolyte. The longer you leave it in the cooling system, the more it will promote galvanic corrosion. The metal transfer eventually causes thinning of the heater core tubes, radiator tubes and deterioration of the water pump.
Coolant contains anti-corrosion additives
All automotive coolants are 92-95% polyethylene or polypropylene based with the remainder consisting of organic or inorganic corrosion inhibitors, pH balancing additives and anti-foaming agents.
Older anti-corrosive additives like silicates and phosphates deposit onto cooling system surfaces to “passivate” the metals to prevent them from becoming anodic. Silicates and phosphates act quickly buy have short lives, so carmakers have turned to organic acid technology (OAT) to prevent cooling system corrosion and extend coolant life.
However, some carmakers prefer a hybrid mix to provide quick passivation yet still provide long life.
S-Hoat is a combination of silicates and organic acid
P-Hoat is a combination of phosphates and organic acid
Water in racing engines
If water is so corrosion, why is it used in race cars? Simple, because it’s drained after each race. The race car benefits from the higher heat transfer during the race, but isn’t affected by corrosion afterward because the water is drained.
©, 2022 Rick Muscoplat
Posted on by Rick Muscoplat