Vehicle belts aren’t that different than the belts that hold up your trousers. They need to fit properly and stay in place, and if they break, sag, or wear out, you’ll probably wish you were wearing a different belt that day. The same goes for the belts in your car. Your engine compartment is a punishing environment, and while all auto belts are made of materials designed to be both flexible and tough, even the toughest materials will eventually wear out due to the extreme temperatures under the hood.