A small pumpless ORC (organic rankine cycle) system with different scroll expanders modified from compressors of the automobile air-conditioner is established, and the refrigerant R245fa is chosen as the working fluid. Different hot water temperatures of 80, 85, 90 and 95 degrees C are employed to drive the pumpless ORC system. Experimental results show that a maximum shaft power of 361.0 W is obtained under the hot water temperature of 95 degrees C, whereas the average shaft power is 155.8 W. The maximum energy efficiency of 2.3% and the maximum exergy efficiency of 12.8% are obtained at the hot water temperature of 90 degrees C. Meanwhile a test rig for investigating the mechanical loss of the scroll expander is established. The torque caused by the internal mechanical friction of the expander is about 0.4 N m. Additionally, another scroll expander with a displacement of 86 ml/r is also employed to investigate how scroll expander displacement influences the performance of the pumpless ORC system. Finally, the performance of the pumpless ORC system is compared with that of the conventional ORC system, and experimental results show that the small pumpless ORC system has more advantages for the low-grade heat recovery. (C) 2015 Elsevier Ltd. All rights reserved.