Numerous things may cause overheating in a vehicle but by understanding how the cooling system works may help you find your problem. Up until the late 1950’s, vehicle cooling systems didn’t operate under pressure. This was primarily because of the vehicles larger radiators and a lot more room under the hood, enabled engines to dissipate more heat. The low horsepower and low compression engines in the older vehicles did not develop a tremendous amount of heat With the advert of higher horsepower engines, smaller radiator (due to styling limitations), higher thermostat opening temperatures and emission controls, this caused much more heat to develop with less surface to dissipate it to the atmosphere. It became necessary to use pressurized cooling systems. By increasing pressure in the cooling system, isolates it from the atmospheric pressure. For every pound of pressure exerted on the cooling system the boiling point (212F) of the coolant is raised approximately 3 degrees F. A cooling system under 15 pounds of pressure will allow coolant to reach 250 degrees F before it can boil. One can now see how important no leaks and a good radiator cap is to the cooling systems of vehicles today. The radiator cap now serves as a vacuum relief and siphon valve allowing coolant to be siphoned back into the radiator as the engine cools and the coolant contracts. Radiator caps also serve as pressure relief valve to prevent excessive pressure in the cooling system after the engine is turned off. Unchecked high pressure could cause damage to the radiator, heater core, hoses or water pump seal. The pressure cap also prevents radiator hoses and tanks from collapsing due to the partial vacuum which would be created if air was unable to enter.