What are the reasons for the obvious decrease in coolant without leakage?

[TylerMarie]

The reasons for the obvious decrease in coolant without leakage include damage to the cylinder head gasket; poor flatness of the joint surface between the cylinder head and cylinder block; warping; and loose cylinder head fastening bolts, which can allow high-temperature and high-pressure gases from the cylinder to enter the cooling system, causing the coolant to be consumed too quickly. How to determine if there is a lack of coolant: Observe the coolant warning light on the dashboard. If it lights up, it is likely due to a lack of coolant, although it could also be caused by excessively high temperatures in the cylinder. Check the coolant reservoir. If the liquid level is below the minimum mark (MIN), do not continue driving and add coolant promptly. Check the water level scale on the coolant bottle. The normal coolant level should be between the maximum and minimum marks. Whether there is a lack of coolant depends on the scale. If the coolant is below the minimum mark, it indicates a lack of coolant.