A coolant level that keeps falling describes what the car is doing, not which component has failed. Similar behavior can come from a mechanical issue, an electrical connection, maintenance condition, or a control-system response.
Start with evidence you can verify: Inspect visible hoses and the ground after parking; a leak can evaporate on hot parts. Replace a part only when a test supports that decision.
Quick educational note
For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.