A fuel dispensing system includes a fuel tank adapted to contain a quantity of fuel. A fuel dispenser in is fluid communication with the fuel tank via piping. A pump is operative to transfer fuel from the fuel tank to the fuel dispenser. A corrosive detection assembly operative to identify presence of a corrosive substance in the fuel is also provided. The corrosive detection assembly has at least one thermoelectric detector positioned to be in contact with fuel vapor in the fuel dispensing system, the thermoelectric detector producing a detector signal indicating presence of the corrosive substance. Electronics are in electrical communication with the thermoelectric detector, the electronics being operative to interpret the detector signal and produce an output if the corrosive substance is present. The at least one thermoelectric detector may comprises a plurality of thermoelectric detectors at different locations in the fuel dispensing system.