Understanding the behaviour of engine and gear oils, especially the viscosity, under temperature and shear is important to improve machine operation. A novel viscometer using ultrasound is presented and used under a range of temperatures. A single cross-temperature (between and ) ultrasonic calibration is shown to be sufficient. Next, the ultrasonic viscometer is compared to a conventional viscosity measurement technique for Newtonian and non-Newtonian lubricants. Newtonian viscosity standard fluids and shear-thinning engine oils are studied. Both viscosity measurement techniques match for Newtonian fluids but ultrasonic measurements are consistently lower for shear-thinning fluids. It suggests that the ultrasonic viscometer is similar to a high-shear viscometer with a shear rate of about 10^6 s-1 .