Sierra's 18-3650 Thermostat Kit fits MCM GM in-line 4 and 6 cylinder engines (1998 and older). The kit contains (1) 18-2831 Thermostat Cover Gasket and (1) 18-3550 Thermostat. It is interchangeable with GLM 13370, Mallory 9-43153, and Mercruiser Stern Drive 59078T3. Each Sierra product meets or exceeds the original equipment part it replaces.