7 Crucial Things to Know About Engine Boilovers

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What causes your engine to boil over and how can you prevent it? Here are seven important facts to know. 

1. Water is the best conductor of heat.

Aside from being the cheapest and easiest fluid at hand when the first engines were created, its ability to transfer heat has made it the default fluid used in cooling systems.

2. Traditional antifreeze is mixed with water, usually in a 50-50 ratio.

Check the bottle your regular antifreeze came in. See the words “prediluted” or “ready to use”? If so, it has already been mixed with water. If it says “concentrate” or “full strength,” you must mix it with water yourself. Either way, 50% of the cooling liquid in your engine is plain old water.

3. Water boils at a relatively low a temperature, and that’s a problem.

Water boils at 212°F at sea level atmospheric pressure. When mixed 50-50 with glycol, the boiling point increases to around 226°F. The back of a bottle of antifreeze will state a boiling point of 256-260°F which is calculated after taking cooling system pressure into account. The problem is that coolant temperature can easily surpass the boiling point of water or water-based antifreeze, and that means the liquid designed to cool your engines will turn to vapor, losing its power to cool.

4. Overheating begins well before the stated boiling point of traditional coolant.

If you’re a motor head (and we’re sure you are), you know that problems crop up well before your engine reaches that 250°F coolant temperature. People tend to get nervous at 215°F, initial problems turn up at 220-230°F, and above 230°F the engine is actively overheating with steam blowing out of the radiator cap.

5. When water becomes vapor, it expands. A LOT.

Water vapor takes up a lot of space when it expands. The force of water turning to vapor can power a steam engine capable of pulling trains across the country. It’s the power behind the electrical generators in a nuclear power plant. It’s a big deal.

6. Vapor can’t cool an engine. And when an engine gets too hot, very bad things happen.

Overheating is a two stage process: first the coolant overheats (boils), then the engine metal temperatures overheat. When antifreeze boils inside the engine, which usually happens around the exhaust valves initially, the vapor pushes coolant away from the metal surfaces. Because it’s no longer being cooled by liquid, the temperature of the metal spikes. The hot spots formed ignite the fuel mixture in the combustion chamber before it’s time (detonation/pre-ignition). When things really get cooking and the exhaust side of the head is super hot compared to the intake side, the head can warp, which ruins the head gasket seal. None of this would happen if the antifreeze hadn’t turned to vapor first.

7. Engines using waterless coolant can handle extreme heat without boiling over.

With Evans coolant, if you see a temperature higher than would be safe with antifreeze, it’s still not a problem. Our coolant performs just as well at 230°F as it did at 190°F. Evans waterless coolants have a boiling point of 375°—well over the operating temperature of an engine, so you never again have to worry when you see the gauge start to climb.