The stem thermometer for diesel engines is a gas pressure thermometer specially designed for the demanding service on diesel engines. The measuring system of the gas pressure thermometer comprises probe, capillary tube and Bourdon spring in a casing. These parts form a unit. The complete measuring system is filled with pressurized nitrogen. A change in temperature causes a change in inner pressure in the immersion shaft. The resulting deflection of the Bourdon tube is transferred to the pointer through a pointer element. The devices are filled with silicone oil and are thus also suitable for service at measuring points exposed to strong vibrations. The fill dampens the measuring system when exposed to mechanical vibrations and thus enables steady indication; it also provides good lubrication for moving parts.