Final answer:
Removing the radiator cap when the engine is warm or hot may cause the coolant to evaporate, leading to a loss of coolant and potential overheating of the engine.
Step-by-step explanation:
Removing the radiator cap when the engine is warm or hot may cause the coolant to evaporate. The high temperature of the engine can cause the coolant to quickly turn into vapor, which can escape through the open radiator cap. This can lead to a loss of coolant and potential overheating of the engine.