KLM Performance carries these OEM Cummins replacement thermostats
When it comes to selecting a replacement thermostat, KLM Performance recommends going with the OEM Cummins thermostat. Each Cummins Replacement Thermostat is built to the exacting standards required for a long and trouble-free diesel engine life. For the safe and secure operation of your diesel engine monitoring the entire engine cooling system is a smart practice. The cooling system is not the place to purchase a low priced part. The purchase of an OEM Cummins Thermostat ensures optimum engine performance and fuel efficiency.
NOTE: Do not operate a diesel engine without a thermostat installed except for servicing or testing of the engine's cooling system. An engine with the thermostat removed will function in the radiator bypass mode. Without a thermostat installed there is no way to regulate coolant temperatures which will cause an overheat condition resulting in severe damage to the engine. If you are now going to replace your engine's thermostat, this is the time to do a complete antifreeze change. We also recommend performing a comprehensive inspection of the cooling system water pump, hoses, and clamps.