Home » Tony’s Tips » Articles » Changing a Cummins Marine 4B, 4BT 3.9, or a 6B, 6BT, 6BTA 5.9 ThermostatChanging a Cummins Marine 4B, 4BT 3.9, or a 6B, 6BT, 6BTA 5.9 Thermostat Front of the Cummins Marine 6BTA Belt Wrap and Thermostat Location on the Cummins Marine 6BTA Un-bolt the Alternator Bracket Swing the Alternator Away Thermostat Housing Bolts Thermostat Housing Lifting Plate Between Housing and Head Thermostat in Housing Remove Hose with Housing OEM Thermostat OEM and SMX 160F Thermostat Cleaned Housing and Plate Rectorseal 5 on Thermostat Seal New Thermostat in Housing Rectorseal on Hardware and Surfaces Rectorseal Mating Surface and Bolt Holes Compliments of a rock solid Boat owner/operator, Robert Schepis