Tests have been carried out to investigate the influence of parameters such as bearing clearance and oil grooving on the temperatures of crankshaft bearings in an automotive engine. Measurements were made in all main bearings and in one connecting rod bearing via a telemetry linkage. All bearing temperatures were found to be very dependant upon oil gallery temperature. Reducing the bearing clearances resulted in increased temperatures in those bearings. Using fully grooved main bearings, in place of partially grooved, produced much higher main bearing temperatures. Reducing the width of the connecting rod bearings resulted in a reduction in their temperatures.