What Causes the Coolant in the Reservoir to Overflow After Parking?

[VonJoshua]

Reasons for coolant overflow in the reservoir after parking: Check if the reservoir cap is damaged. High temperature inside the reservoir can cause coolant to leak if the cap is damaged. Overfilling the coolant—if the coolant level exceeds the marked line on the reservoir, it may lead to overflow. Thermostat failure can cause the engine temperature to rise excessively, preventing the coolant from circulating properly through the engine's cooling system, resulting in overflow during minor circulation in the radiator. Additional information: Note: When the engine temperature rises, the coolant expands, and some may flow into the overflow reservoir through the radiator cap. As the temperature drops, the cooling system's pressure draws the coolant back into the radiator. The overflow reservoir has marked lines; overfilling the coolant can cause overflow. These lines also help indicate whether the current coolant level is sufficient.