Engine Overheating Is your engine overheating? Most engines are designed to operate within a "normal" temperature range of about 195 to 220 degrees F. A relatively constant operating temperature is essential for proper emissions control, good fuel economy and performance. But problems can arise that cause the engine to run hotter than normal, resulting in engine overheating. Your engine's cooling system is filled with a 50/50 mixture of water and ethylene glycol antifreeze. The coolant will boil at 225 degrees unless it is held under pressure by the radiator cap. A 15 PSI radiator cap will increase the boiling temperature of a 50/50 coolant blend up to 265 degrees F. If the concentration of antifreeze to water is upped to 70/30 (the maximum recommended), the boiling temperature with a 15 psi radiator cap goes up to 276 degrees. So obviously the radiator cap plays a significant role in preventing the coolant from boiling and the engine from o