Why is the coolant not circulating in the radiator?

The coolant may not be circulating in the radiator due to several reasons, including a malfunctioning water pump, a clogged radiator or hoses, or a stuck thermostat. Additionally, low coolant levels or air trapped in the system can also impede circulation. It's essential to diagnose the issue promptly to prevent overheating and potential engine damage. Regular maintenance can help identify and resolve these issues before they become serious.