A process for heating thermally unstable or difficult to heat liquid feeds, e.g., used lubricating oil (ULO) to dehydrate and/or recover distillable components therefrom, is disclosed. The liquid feed is heated by direct contact heat exchange with molten salt, preferably maintained as a bath, operating at a temperature above the boiling point of water and below 600 C. The liquid feed is heated and typically at least partially vaporized in, or above, or by contact with the molten salt to produce a heated liquid. When ULO contaminated with water is the feed, the vapor product of the process will comprise water vapor and/or distillable hydrocarbons. ULO additive decomposition products, such as carbon, may be removed as a solid, semi-solid or liquid residual phase from contact with the molten salt.