Maximize Johnson/Evinrude outboard performance and efficiency by running at the optimum temperature. A failed thermostat can cause an engine to run at outside of its optimum temperature and can adversely affect performance and efficiency. The fix can be as simple as replacing the thermostat. This Sierra thermostat is engineered with a temperature rating of 143F (62C) and is compatible with almost 5000 Johnson/Evinrude outboard models. Key Features Thermostat meets or exceeds manufacturer specifications Temperature rating of 143F (62C) Compatible with almost 5000 models of Johnson/Evinrude outboard engines; with your outboards serial number use our Engine Part Selector or call 1-800-BOATING to confirm this thermostat is correct for your outboard 18-3540 Application Guide. ApplicationOEM Part NumbersJohnson/Evinrude Outboard393659, 434841, 378065, 508626, 5005440, 437414The Sierra Engine Parts SelectorIn addition to thermostats, we offer a wide variety of other engine parts manufactured by Sierra. To see if we have the part you need, see ourEngine Parts Selector, where you can search by engine make, serial number and model or year of manufacture