Your car has been sitting for a few weeks, and suddenly you notice that the brake rotors are rusty. Instead of kicking the tires and worrying about the amount of money you're going to have to spend on new rotors, check first to find the cause of the problem and maybe even a cheaper solution.
Take a closer look. Rust occurs when too much moisture has a chance to chemically react with the metal on your rotors, and generally it only occurs if the car has enough time to sit and rust.
Check out the brake pads. If your vehicle has been sitting for a while, take a look at the brake pads and the surface of the rotors. If the pads don't seem to have rust residue on them, chances are, the rust is mostly superficial. If the rotors only have rust on the surfaces exposed to the air, as opposed to large patches of rust, your rotors are merely responding to the elements.
Consult your calendar. Rusted brake rotors will cause a problem, but if the rust seems superficial, the reason for the rust might purely be a result of not properly drying your vehicle. Rain, snow, or driving in a flooded areas can also cause this.
Drive your vehicle. If you detailed your vehicle and then let it sit for a week or more, take the car out. If a few weeks ago your brake rotors weren't rusted, the brake pads will remove the rust when you drive the car. If the rust on your brake rotors looks like its eating your rotor, then you need to replace it.
Check the rotors out on each of the brakes and diagnose bad each is rusted out before you replace all of the rotors, as only one or two may be seriously affected.
