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Temperatures of three bearing and seal parts of a swash plate type axial piston pump were measured simultaneously using a slip ring with thermocouples' amplifiers. The rotating cylinder block had five thermocouples, the swash-plate had four, and the valve-plate had four. Three sets of pistons with different diameters were prepared. Hydraulic mineral oil with VG22 and a water–glycol type hydraulic oil with VG32 were used as test fluids. The maximum discharge pressure was 20 MPa; the maximum rotational speed was 25 rps. The inlet oil temperature was 20-40°C. Temperatures and temperature differences between the bottom-dead-center and the top-dead-center increased concomitantly with the discharge pressure. For larger piston clearance ratios, the temperatures rose monotonically. The bearing and seal parts were markedly hotter than the discharge oil. Temperatures rose much less using the water–glycol type oil than when using the mineral oil.