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Automotive cooling systems have been designed to operate in excess of 100C for decades now. The system is designed to pressurize the coolant to raise the boilin

by cc439 9y ago

Automotive cooling systems have been designed to operate in excess of 100C for decades now. The system is designed to pressurize the coolant to raise the boiling point by as much as 25C/45F. The radiator cap acts as a pressure release valve and most are typically designed to blow at 15psi above atmospheric pressure. You also have the intended working temperature of ICE and eletric powerplants inverted. While an ICE's cooling system is designed to keep maximum coolant temperature around 110-115F, the internal components are designed to operate far in excess of that temperature. Exhaust valves, for example, are designed to operate indefinitely at temperatures exceeding 700C with the valves of high performance engines nudging 900C. Electric motors on the other hand, rapidly lose efficiency as operating temperature increases.

Retric 9y ago
Radiator sizing only cares about the working fluid temperature, temperatures past that point are irrelevant. Anyway, remember failure point != safe operation. 50/50 antifrease mixture generally boils at 220f at 1atm. As you say assuming nothing is wrong up to 265f is possible to maintain, but operating temperatures are generally kept below the boiling point for several very good reasons. Critically, the engine should operate even if the cooling system has a minor leak as long as it's working fluid is topped off.
- sudojudo 9y ago
  Every modern IC engine (and the majority of old ones) operates with a pressurized cooling system; they absolutely will not function properly with a leak. The average operating temperature of engine coolant is around 200F, the only reason it doesn't boil over is because of the aforementioned pressure, which is usually around 15PSI (bringing the boiling point to just above 250F). The rating on 50/50 antifreeze relies on coolant system pressure, it (ethylene glycol) will boil like water if put on a stove. The key to antifreeze is in its name: anti-freeze. It does raise the boiling point of water a little, but that's just a side benefit and is of no real significance (plain water transfers heat better). These readily available facts contradict the comment above. The person is certainly trying to make a point, but they seem to have the fundamentals completely wrong.
  - Retric 9y ago
    200F is only 93C which is below the boiling point. This is very much by design. Yes, the coolant loop is designed to be operated under pressure, however being able to drive with a coolant leak under sub optimal conditions is very important. Further, engines are designed to operate at unusually high external temperatures as temperatures up to 134f / 56.7°C have been recorded, though not nessisarily with a leak. Note, road surfaces can be significantly above ambient temperatures.
    - sudojudo 9y ago
      No cars, in the real world, are driving around with significant coolant leaks. End of story. Talk to any repair shop. That's the crux of my argument. There is no scenario where one can continue to drive a car with a coolant leak. This kills the engine. Our discussion feels like a mechanic arguing with an engineer. Probably because that's exactly what's happening.

by cc439 9y ago

Retric 9y ago

Radiator sizing only cares about the working fluid temperature, temperatures past that point are irrelevant. Anyway, remember failure point != safe operation. 50/50 antifrease mixture generally boils at 220f at 1atm. As you say assuming nothing is wrong up to 265f is possible to maintain, but operating temperatures are generally kept below the boiling point for several very good reasons. Critically, the engine should operate even if the cooling system has a minor leak as long as it's working fluid is topped off.

sudojudo 9y ago
Every modern IC engine (and the majority of old ones) operates with a pressurized cooling system; they absolutely will not function properly with a leak. The average operating temperature of engine coolant is around 200F, the only reason it doesn't boil over is because of the aforementioned pressure, which is usually around 15PSI (bringing the boiling point to just above 250F). The rating on 50/50 antifreeze relies on coolant system pressure, it (ethylene glycol) will boil like water if put on a stove. The key to antifreeze is in its name: anti-freeze. It does raise the boiling point of water a little, but that's just a side benefit and is of no real significance (plain water transfers heat better). These readily available facts contradict the comment above. The person is certainly trying to make a point, but they seem to have the fundamentals completely wrong.
- Retric 9y ago
  200F is only 93C which is below the boiling point. This is very much by design. Yes, the coolant loop is designed to be operated under pressure, however being able to drive with a coolant leak under sub optimal conditions is very important. Further, engines are designed to operate at unusually high external temperatures as temperatures up to 134f / 56.7°C have been recorded, though not nessisarily with a leak. Note, road surfaces can be significantly above ambient temperatures.
  - sudojudo 9y ago
    No cars, in the real world, are driving around with significant coolant leaks. End of story. Talk to any repair shop. That's the crux of my argument. There is no scenario where one can continue to drive a car with a coolant leak. This kills the engine. Our discussion feels like a mechanic arguing with an engineer. Probably because that's exactly what's happening.