Generac 0H41040239 2.4L Diesel Thermostat.
For thermostat gasket, see here: Generac 0H41040222 2.4L Diesel Thermostat Gasket
Generac replacement parts will also usually fit the following Generac branded generators: Honeywell, Guardian, Siemens, Carrier, Watchdog, Centurion, Eaton & Bryant.
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