Observable states for the polycation-anionic/nonionic mixed micelle system PDADMAC-SDS/TritonX-100 include: soluble complexes, liquid coacervates, and precipitates. The corresponding transitions were studied as a function of [SDS]/{[SDS]+[TX100]} = Y, temperature (T), ionic strength (I) and polycation MW. Phase separation (at T_φ) is induced by an increase in T, a decrease or increase in Y or I, and is favored by high MW. At fixed I, the T_φ -Y boundary comprises: (A) a coacervation domain exhibiting an LCST, and (B) a superimposed precipitation or high-density coacervation domain. Region A is symmetrical around 0.2<Y*<0.6 where charge-neutralized complexes/aggregates are at incipient phase separation. In region B (high Y) the dependence of the phase boundary on I, MW and Cp is consistent with polycation collapse and counterion expulsion. Coacervates formed in region A, which were found to undergo further phase separation at T_φ' (> T_φ) , were characterized by turbidimetry, light scattering and rheology, with the following results: (1) Microphase separation along elongational shear lines is seen at (T_φ'-T)=2oC - 8oC, where coacervates are shear-thinning. (2) Coacervates display a dominant slow mode in DLS which increases as temperature rises above T_φ', along with a low-intensity temperature-independent fast mode corresponding to nearly free micelle diffusivity. (3) At T ca. 2-3oC above T_φ', a plateau appears in shear stress vs. shear rate curves. The results are consistent with mesophase separation within the coacervates driven by the entropy of counterion release. The enhancement of this process by shear is not yet fully understood.