A simple and general method for applying the results of a microinstability analysis to models of the solar wind is described. Existing two-fluid models are found to become unstable at heliocentric distances varying from 3 to 11 Rs. The development of these 'heat conduction' microinstabilities affects the energy and momentum transport, observable wave spectrum, cosmic ray diffusion, and properties of minor ions in the solar wind. A proposal which would rationally modify the energy transport is developed. It is suggested that the plasma fluctuations observed near the earth could largely be a result of these instabilities. The observed temperatures and velocities of helium ions can be explained qualitatively in terms of resonant interaction with the different waves which are expected to be generated under different solar wind conditions.