Sierra 18-3550 Thermostat for Mercury/Mercruiser Inboard/Outboard Marine Engines 59078 Thermostat for Mercury/Mercruiser Inboard/Outboard Marine Engines Replaces: Mercury 59078 and GLM 13020 Temperature Rating: 140 Degrees Sierra Part Number 18-3550 All Sierra parts qualify for and are covered under Sierra's Industry Leading Customer Satisfaction Warranty Before Ordering, Please Verify this is the Correct Part for your Application. For Assistance, Please Call Sierra's Tech Support at 1-877-663-8396