Don t sacrifice performance by running the engine too hot or too cold A failed thermostat can cause an engine to run at the wrong temperature adversely affect performance and efficiency. The fix can be as simple as replacing the thermostat. Sierra engineered this thermostat to meet or exceed the specifications for many GM based applications that require a 160 degree operating temperature (1987 and newer with standard cooling systems). For 50 years Sierra has been producing parts engineered to meet or exceed the specifications of marine engine manufacturers and has gained the confidence of engine manufacturers and boat builders. Boaters and technicians can be assured a Sierra part will fit right the first time and restore function to OEM specifications.