Diagnosing the thermostat using vehicle on-board diagnostic (OBD) data

The thermostat is a crucial component of a car's internal combustion engine's cooling system. Failure of the thermostat can result in undercooling or overheating of the engine. Undercooling may increase wear of engine components due to poor lubrication and lead to higher fuel consumption. Conversely, overheating can damage the engine. The engine coolant temperature is one of the fundamental parameters for the proper functioning of the engine. The vehicle's onboard diagnostics system was unable to detect the malfunction of the thermostat. As a consequence, fuel consumption increased, which was especially noticeable in winter. This paper evaluates the possibility of carrying out thermostat diagnostics using data obtained from the OBD system through a diagnostic interface ELM327, which is connected to the OBD-II connector and interfaced with Torque Pro software on a smartphone. Analysis of the data confirmed that the proposed diagnostic method was appropriate. Furthermore, the impact of the thermostat malfunction on different factors such as coolant temperature, cold engine warm-up time, parameters characterising thermostat cycling, and fuel consumption of the car were studied. It was found that, apart from the already mentioned decrease in coolant temperature, the thermostat hysteresis also decreased and the thermostat cycle time increased.