Thermostat used on various Mercruiser fresh water cooled inboard marine engines. 160 Degree Thermostat | Sierra 18-3552 Fits Mercruiser 470 model 4 cylinder closed cooled engines from 1976 to 1982 with serial number range 420873-6218036 Fits Mercruiser 485 model 4 cylinder closed cooled marine engines with serial number range 5685934-6218036 Replaces Mercury 76270T Replaces Mallory 9-43000