If your coolant looks rusty, it's likely because there's rust in your cooling system. Rust can enter the system through the water pump, radiator, or engine block. Once it's in the system, it can cause corrosion and clogging.
Rust is a major problem for cooling systems because it can cause a lot of damage. It can lead to engine overheating, premature failure of parts, and reduced efficiency. In some cases, rust can even cause complete engine failure.
If you notice rust in your coolant, it's important to have the problem checked out by a mechanic as soon as possible. They will be able to flush the system and replace any parts that are damaged by the rust.