It occurs because the hose, liquid coolant (ethylene glycol antifreeze and water), and the engine/radiator fittings form a galvanic cell or "battery.". GATES Radiator / Curved Hose. Give a Good Squeeze to a Bad Hose.
Made of steel and thermoplastic, Gates DriveAlign® idler/tensioner pulleys provide excellent wear resistance, heat dissipation and dampening. They resist dust, grit, salt, and other contaminants that reduce pulley life.