A mathematical model to predict the dynamic behavior of two-phase mechanical seals, including the effects of thermal coning and face contact but, neglecting squeeze film effects, has been constructed. Numerical results for a representative seal indicate that such a seal is sensitive to finite disturbances which can trigger an oscillatory instability, even when operating at an equilibrium point with positive stiffness.Presented at the 45th Annual Meeting in Denver, Colorado May 7–10, 1990