Upgrade the thermostat housing in your 5.9L or 6.7L Cummins allowing you to customize your coolant routing with the Fleece Performance Thermostat Housing With Auxiliary Port. This is the same thermostat housing that is used in Fleece's Coolant bypass kits and features an auxiliary port with plug. The auxiliary port is threaded to accept a -10AN (7/8"-14) fitting to allow you to customize your coolant routings and includes port plug if unneeded. The cast aluminum construction provides strength and the Fleece logo will add a custom look to your engine bay.