At least one thermal imaging camera mounted or positionable in a location that enables the camera to capture a thermal image of at least part of one lateral side of a harvester when the harvester is operational in a field. The camera may for example be mounted on a movable component or subsystem of the harvester, such as the unloading tube of a combine harvester according to an embodiment of the invention. When the unloading tube is in the unloading position, the camera is enabled to capture an image of the unloading side of the harvester. The system further includes a processing unit and a control unit, configured to process and analyze captured thermal images, and compare temperature-related parameters derived from said images to a threshold.