Despite its increasing popularity as a continuous professional development tool in ELT contexts, why teacher research remains as a minority activity and whether or how its impacts persist over time still require detailed exploration. In this mixed-methods case study of university instructors in Turkey, we address the questions of teacher research engagement and sustainability of its impacts. The study started with a relatively larger group (n=33), and then gradually narrowed into three sub-groups to gain an in-depth understanding of the case. Two questionnaires consisting of closed and open-ended questions and interviews carried out with semi-structured forms have been used as data collection tools. The qualitative data have been analyzed by content analysis, while frequency analysis has been carried out for the quantitative data. Findings reveal that expert support and colleagues with research experience trigger teacher research engagement, whereas limitations in institutional support and instructors' awareness of teacher research and economic matters contribute to the most prevalent barrier to teacher research viz. lack of time. Moreover, instructors feel more motivated and confident, research-oriented four years after their teacher research projects. We argue that positive experience with context-related research projects and dissemination of research results in various forms facilitate the sustainability of those impacts and efforts to engage in new projects, while constraints in time and institutional support hinder these. [This study was presented at 7th International Congress on Curriculum and Instruction (ICCIEPOK, 2019) in Ankara, Turkey.]