Here are some reasons why you might want to change the thermostats in a Cummins engine:

1.     Overheating: The thermostat regulates the flow of coolant through the engine. A faulty or worn thermostat can cause the engine to overheat due to inadequate coolant circulation.

2.     Reduced engine performance: If the engine is running too hot or too cold, it can result in reduced engine performance and power.

3.     Poor fuel economy: If the engine is running too cold, it can result in poor fuel economy due to incomplete combustion and increased fuel consumption.

4.     Failed emissions test: If the engine is running too cold, it can result in increased emissions, which can cause the engine to fail an emissions test.

5.     Maintenance: Over time, the thermostat can become worn or clogged with debris, which can lead to reduced efficiency and performance. Regular replacement of the thermostat can help prevent these issues.

In summary, the thermostat is a crucial component of the engine’s cooling system, and it needs to be in good working order to ensure optimal engine performance and prevent engine damage due to overheating. Regular maintenance and timely replacement of the thermostat can help prevent issues that may require thermostat replacement.