What should I do if the water in the car tank turns yellow?

This is usually caused by scale or rust. Before adding water to the water tank, you must use special cooling water, and you can't add cooling water indiscriminately. Excessive cooling water will cause fouling or rust in the engine water tank. Buy a bottle of water-ballast cleaning agent, add it and run it at idle speed for ten minutes, then let it all go, and add good quality antifreeze.