text: highest temp of most cars?   are you referring to operating temperature of the engine?  it depends on where you are measuring it.  inside the cylinders, oil temperature, coolant temperatures...they're all different.  since most dashboard temperature gauges refer to coolant temperature, i will elaborate a little bit on that.  normal operating temperature for engine coolant is typically 180-195°f and is regulated by the coolant thermostat (usually a bimetallic controlled valve).  coolant can get up to about 240°f before serious problems begin to develop (such as boiling).  this is because the coolant is not entirely water, and it is under slight pressure, which raises the boiling point of the coolant.