Abstract: A thermal warning device attaches to a wheel assembly of a railway car to detect whether the wheel assembly has reached high temperatures and may lead to a potential bearing failure. A temperature sensor for monitoring the temperature of the wheel assembly is coupled to an electronic circuit for determining whether a bearing failure may occur based on the temperatures detected by the temperature sensor. In particular, the temperature sensor adjustably extends into the wheel assembly in order to obtain accurate readings of high temperatures in wheel assembly. Also, the electronic circuit is situated away from the outer surface of the wheel assembly so that the electronic circuit will not be subjected to heat from the wheel assembly and may freely dissipate heat produced by its own components. Upon determination of a warning condition, the electronic circuit transmits a warning signal to a wayside station or train crew.