With the increasing complexity of the engineering role, todays graduates must be capable of confronting both technical and societal problems; underpinned by effective teamwork at their core. Problem-based learning has been implemented in engineering to better prepare students for modern industry. However, limited research has examined the complex social processes involved in PBL. The present study, therefore, reports on how students working in tutorless PBL groups - owing to teaching limitations - must effectively self-manage their team efforts if they are to succeed. This PBL arrangement involved a floating facilitator but the analysis focuses exclusively on the students tutorless interactions. The data collected is from 22 chemical engineering undergraduates in four groups, and consists of naturalistic video-recordings of 32 PBL meetings (35 h). This corpus was examined empirically using conversation analysis to elucidate students recurrent communicational practices. The microanalyses showed how students continuously established PBL as the collective responsibility of the group. Furthermore, students maintained average, equal social identities, and used humour/self-deprecation in constructing an informal learning environment. In the absence of the tutor who would normally maintain cohesion, these strategies offer a means through which students adapt to the unfamiliarity of the tutorless setting, where no member is positioned as the substitute tutor.