Abstract Recent results of power generation experiments with an improved heat exchanger system in the FUJI-1 facility were described. One of the main purposes was to study the effect of working gas temperature on generator performance. The results with argon working gas showed that the gas temperature of 1850 K is enough to eliminate the effect of inlet relaxation under the present experimental conditions and that gas temperature does not greatly affect the output performance so long as the inlet relaxation is not significant. The radial component of velocity was successfully measured with high time resolution by means of the cross-correlation method. The effect of seed fraction on the measured velocity was discussed. For the case of helium working gas, the voltage drop owing to an inlet relaxation was remarkably decreased, and improvement in both output power and enthalpy extraction can be observed by the increase of gas temperature. The voltage drop still existed at the inlet of the channel, and therefore, higher gas temperature and higher seed fraction are required in order to achieve higher generator performance.