Why is the water boiling over in your car but it is not marking hot?

The boiling point of water is 212 degrees, most vehicles now days operate ftom 205 to 215. A 50% mix of distilled water and antifreeze will extend the the boiling point to 265 degrees at sea level. If you go up in elevation the boiling point will decrease, so make sure you have a known good or new radiator cap to prevent premature water boiling in higher elevations