Using self-generated analogies has been proposed as a method in a constructivist tradition for students to learn about a new subject, by use of what they previously know. We report on a group exercise on using self-generated analogies to make sense of two thermodynamic processes, reversible adiabatic expansion and free adiabatic expansion of an ideal gas. The participants (N = 8) were physics preservice teacher students at the fourth year of the teacher education program. A main finding was that work with self-generated analogies tended to be accompanied by the students assuming ownership for their learning, manifested in terms of actions of choice and control and the use of exploratory talk. Consequently, several self-generated analogies were elaborated and developed to a high-order relational structure. However, we also found that with the use of self-generated analogies in science teaching follows the risks of developing idiosyncratic explanations of the encountered phenomena or getting stuck in overly complex comparisons. (Contains 2 tables.)