Interstellar pickup ions, if they are thermalized, could produce a longitudinal asymmetry in solar wind temperature in the outer heliosphere. Between 1978 and mid-1992, the Pioneer 10 and Voyager 2 spacecraft were well situated to search for such an asymmetry. Pioneer 10 was headed downstream with respect to the local interstellar medium while Voyager 2 was headed upstream. Both spacecraft were at large heliocentric distances; by mid-1992, Pioneer 10 was at 55 AU, while Voyager 2 was at 37 AU. Measurements from these spacecraft and the Pioneer Venus Orbiter are complicated by solar cycle effects but suggest an upper limit of 5000 K for any asymmetry that might be present. These measurements are also consistent with no asymmetry. There is also some suggestion that the radial profile of solar wind temperature in the vicinity of the solar equator was steeper during the declining phase of the last solar cycle. The solar wind temperature has increased at Voyager 2 after mid-1992, but Voyager 2 has also been moving to higher heliographic latitudes, where such an increase should be expected from the well-known latitudinal gradient in solar wind temperature that has been observed by Pioneer 11 and Ulysses.¿ 1997 American Geophysical Union