In the presence of electrostatic or electromagnetic fields, the viscometric thermometer is one of the few possible and feasible methods of temperature measurement. The device can be operated in a constant pressure or a constant flow mode. The former system is simpler and easier to build and operate but it requires a relatively long reading time of 1 to 2 min and, consequently, can be used only in ‘‘steady‐state’’ flows where the variations in temperature are much slower than the reading time required. Different configurations and measurement procedures are described. In particular, a viscometric thermometer was designed and built for the constant pressure mode which enabled us to obtain the temperature distribution inside the channel of an electrohydrodynamic pump.