The coolant in a vehicles radiator can run hotter than 212f ( boiling
point ) due to the system being pressurized and the boiling point of the
coolant is higher under pressure. A vehicle's cooling system is typically in
the range of 11 to 15 lbs of pressure in it, determined by the radiator cap,
which would allow a vehicle to run much warmer than 212f before the coolant
The primary purpose of the thermostat is to get the engine to normal
operating range as quickly as possible. This reduces wear, improves
efficiency, and reduces pollutants. The latter was a primary driving
force in increasing engien operating temperaturesd. As an aside, it
also gets the water hot for the heater/defroster. I don';t know what
the boiling point the new delco coolants are, I suspect at least as high
as ethelyne glycol/water mix. A 50/50 mix has a boiling point around
225-230 F at sea level. Each pound of pressure on the system adds about
1 degree F to the boiling point so the boiling point of a system with a
15 lb cap at sea level running half ethelyne glycol at sea level is in
the neighborhood of 245 to 250 degrees. The transfer of heat from the
coolant to the air in the radiator increases with increased temperature
differential so the radiator size can also be reduced.
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