what coolant temp is too high

The safe limit for engine coolant temperature depends on the coolant that youre running, the concentration, and the setting of the pressure cap. Assuming a fairly standard coolant, diluted 50/50 with water, and a 15 PSIG cap, youre looking at around 265° F or 130° C before things start to boil. Most engines are designed to run with coolant temperatures between 160 degrees and 200 degrees. If temperatures in your engine stay too cool, combustion will have to be too rich to keep things running smoothly. If temperatures get too hot, the coolant can start to boil, reducing its ability to cool the engine and possibly causing damage to the engine and its components. Although your vehicle may still run when the temperature is too high, you will be causing unseen damage to the engine. Lack of coolant leads to the breakdown of the engine due to overheating, so the quality and quantity of the coolant need to be inspected at regular intervals and replaced with a suitable substitute if necessary. If the coolant gets too hot, the engine may overheat, and the coolant temperature warning light may come on.