After replacing a coolant thermostat, the engine overheats. What could be a likely cause?

When an engine overheats after a coolant thermostat replacement, the issue of air trapped in the cooling system is a likely cause. During the thermostat replacement process, it's common for air to enter the cooling system, especially if the system wasn't properly bled afterward. Air pockets can create blockages in the coolant flow, preventing it from circulating efficiently through the engine and radiator. This lack of proper coolant circulation leads to overheating.

While other problems can cause overheating (such as a malfunctioning radiator fan, a faulty thermostat, or insufficient coolant levels), the specific context of replacing the thermostat often highlights air entrapment as a primary concern. Ensuring that any air is properly bled out of the system after a thermostat or any cooling system component replacement is critical to maintaining appropriate engine temperatures.