It may not build pressure right away. The coolant wont even move much until the thermostat opens. But, with the radiator cap off, there will not be any pressure at all, nor should there be. The cooling system is designed to work under pressure, though. Usually 13 to 16 lbs. For every pound of pressure, the coolant 'gains' 2 degrees of boiling point. So, doing the math, if water boils at 212 degrees under NO pressure, and the cooling system is under 15 lbs of pressure, that would add 30 degrees to the boiling point of the coolant. Now the coolant won't boil til it gets to 232 degrees, which is OVER the recommended temp. There is nothing on the car that 'builds' water pressure. The pressure is built on it's own due to temperature. That's just how it's designed. As the coolant gets hotter and hotter, the pressure rises on it's own, thus increasing the boiling point. Therefore, the cooling system does it's job. Most cars today are designed to operate at about 210 degress or so. Hope this helps ya. If I'm way off base with you, let me know and I'll try again.
Apr 4, 2009 at 2:16 PM
