System and method for constantly monitoring the state of the oil of the wheels of heavy machinery, in particular mining trucks, while they are in motion. Comprising a server; a wireless sensor module attached to the rim of the wheel, obtaining oil measurements from an oil quality sensor, which sends the measurements to the server wirelessly; the sensor, located inside the sensor module; and a spoon-type mechanism which maintains the sensor in permanent contact with the oil inside the wheel, wherein said spoon-type mechanism rotates with the sensor module and the wheel. In addition, it may comprise a receiving antenna module which is located between the sensor module and the server. In addition, it may comprise a transmitter which is located between the receiving antenna module and the server.