Abstract: A test device for assessing low temperature performance of a wax-containing fuel which compriss: a vessel for containing a fuel to be assessed, having cooling and heating elements, for cooling and heating the fuel in the vessel and a filter element wherein the fuel is caused to pass through the filter of the filter element and the cooling and heating elements are so arranged that a stable convection current is set up in the fuel and the filter is so positioned that it receives wax settling from the fuel.

Abstract: The state of mobility of a substance--e.g., the pour point of a liquid, is determined by disposing in or in contact with the substance a shear device at the bottom end of a substantially vertical elongate probe mounted for rotation about its vertical rotational axis. The probe is urged to a datum position by suitable means (e.g. a pair of magnets) and, intermittently, a rotational force is momentarily applied to the probe at its top end to cause rotation about the probe axis away from the datum position. If the probe rotates, because the mobility of the substance so permits, a member attached to the probe interupts a light path between a light source and a light sensor, giving rise to a signal indicative of the mobility of the substance. When there is no, or slow, rotation, the non-interruption of the light path over a selected time interval indicates a reduced mobility of the substance.