If after a detailed inspection, nothing has become evident, then you can suspect that the cause of too much coolant use by the vehicle is temporary overheating or long-term maintenance neglect. To determine the coolant level, check the reservoir and not the radiator of the vehicle.
Why does my coolant fluctuate?
The coolant inside a car's cooling system drastically fluctuates in temperature, which means its volume also changes. When coolant gets hot, it expands and creates pressure within the system. Once the radiator is completely full, this expanding hot coolant will overflow into the reservoir.