A positive-displacement sliding-vane pump was tested separately with trichlorofluoromethane (i.e. R-11) and trichlorotrifluoroethane (i.e. R-113), each being a short-listed, attractive organic working fluid for a Rankine-cycle low-grade energy engine. The experimental results showed that the pump performed better with R-113 than with R-11. The addition of 10 per cent (by mass) of Clavus oil 68 into the fluids further improved the pump's performance.