Review on 🔧 ACDelco GM Original Equipment 131-131 Engine Coolant Thermostat: Efficient Cooling Solution for Optimal Engine Performance by Vivian Eker

For the LB7 (early 2000's) Duramax you will need two different thermostats that fit in the same housing. There is no traditional case gasket - thermostats have a rubber gasket around the perimeter that acts as a seal. I've had this truck for 13 years since it was new and it has never come anywhere close to normal operating temperature when the ambient temperature is below about 50 degrees Fahrenheit. I replaced those thermostats and now the truck is approaching summer engine temp pretty quickly. even with an ambient temperature of around 30 degrees, which is about as cold as here. The thermostats aren't marked AC Delco, but they look identical to the factory parts and work better, so I'm happy.