Wouldn't the pressure in the closed cooling system remain the same?
Whatever the cap release pressure is?
Paul
Smit, Theo wrote:
> The ambient air pressure goes down with altitude; the average pressure
> in Calgary (altitude 3500ft) is about 90% of sea level pressure. The
> oxygen content (by volume percentage) is still around 20-21%, but
> engines up here don't make the same amount of power as they do at sea
> level due to the reduced ambient pressure. You could compensate by
> increasing the compression ratio - assuming you never take the car
> anywhere lower in altitude. Turbochargers with the waste gate referenced
> to absolute pressure are the way to go - constant performance regardless
> of the ambient conditions.
>
> As it relates to cooling: You're making less power at altitude so the
> engine doesn't make as much heat. However, the air massflow through the
> radiator is lower because the air density is lower, so the cooling
> effectiveness is similarly reduced. The cooling system is limited to
> (say) 13 PSI over whatever the ambient pressure is by the radiator cap,
> but that's almost one full atmosphere (14.7 psi nominal) over ambient,
> so the boiling point of the coolant is only fractionally reduced as a
> result of the decrease in ambient pressure.
> As an example, in Calgary, the boiling point of water is about 96.5
> degrees C, where it would be 100 degrees at sea level. If you're running
> your car within 3 degrees (that's about 5 or 6 degrees Fahrenheit) of
> boiling over, then you're too close anyway.
>
> Best regards all,
> Theo
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