I have 2008 Dakota 4.7. Chk engine light comes on throws code 128. Have replaced thermostat and sensor, light still comes on and later goes off by its self. Never has over heat....Can not figure what replace next.

 

If I am correct and if not someone please correct me, but a PO128 could mean the engine is not reaching normal operating temperature. If that is the case it is possible the fan is running too much/too early. Also have you checked the coolant level?
Some more info that may help is how long of driving does the light come on and how long before it goes off?

 

Not an electric fan. Coolant level is proper and new.

 

I just looked at Alldata, and there's a huge diagnostic tree to deal with P0128. Here's the summary chart.