Analysis of data obtained by Ogo 5 confirms the Imp 6 observations of the inverse dependence of the helium to hydrogen temperature ratio THe/TH on &tgr;e/&tgr;c, the ratio of the solar wind expansion time to the Coulomb collision equipartition time. The difference between the absolute values of the averages of THe/TH as observed by Imp and Ogo is probably due to the difference of the weights given to high- and low-velocity periods by the two experiments. The magnitude of the differential flow vector Δv=‖vHe-vH‖ varies inversely with &tgr;e/&tgr;s (where &tgr;s is the Coulomb collision slowing-down time) when &tgr;e/&tgr;s is small and approaches zero when &tgr;e/&tgr;s is large. The data suggest a model of continuous preferential acceleration and heating of helium (or deceleration and cooling of hydrogen) which is opposed and limited by Coulomb collisions. Since the average dependence of Δ&ngr; on &tgr;e/&tgr;s cannot explain all of the systematic variations of Δ&ngr; observed in corotating high-velocity streams, extra helium acceleration (or hydrogen deceleration) probably occurs on the leading edge of such streams.