What are the reasons for slow engine coolant temperature rise?

[DelGenevieve]

The slow rise in engine coolant temperature is caused by a faulty thermostat. The working principle of the thermostat is: 1. When the vehicle's temperature has not yet reached the normal operating temperature, the thermostat remains closed. At this time, the engine coolant returns to the engine via the water pump, creating a small circulation loop within the engine to facilitate rapid warm-up; 2. Once the temperature exceeds the normal operating range, the thermostat opens, allowing the coolant to circulate through the entire radiator circuit for large circulation, achieving rapid heat dissipation. The thermostat is an automatic temperature-regulating device containing a temperature-sensitive component. It automatically adjusts the amount of coolant entering the radiator based on the coolant temperature, altering the circulation range of the coolant to regulate the cooling system's heat dissipation capacity.