If your engine isn't getting up to full operating temp regularly, it will have a harder time getting rid of the the moisture, fuel and other unwanted things that are floating around in the engine oil and crankcase. It might degrade your engine oil ever so slightly faster. But that will probably take a long time for that to be an issue. It might also be a little bit less efficient. Cylinder wall and combustion chamber temps do affect the combustion. Although you're not significantly off of the ideal operating temp range.

For the time being, it's definitely ok to drive. Get it fixed when you're able to. Otherwise carry on and enjoy.

 

It's okay to drive for a little while. It's probably either the thermostat or the temperature sensor, and the thermostat is inexpensive and easy to replace.

 

A code P0128 may mean that one or more of the following has happened: Low engine coolant level Leaking or stuck open thermostat (likely) Faulty cooling fan (running too much) Faulty coolant temperature (ECT) sensor Faulty intake air temperature (IAT) sensor Possible Solutions Note: Please be sure the engine is turned off and cool when doing work on the cooling system. When the engine is warm, the cooling system is pressurized and very hot and can cause burns or other personal injuries if you are not careful. Past experience indicates that the most likely solution for a P0128 is to replace the thermostat.

However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code: Verify coolant strength & level Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary. Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary. Verify proper intake air temperature (IAT) sensor operation, replace if necessary. If the above items check out good, replace the thermostat.

Read more at: P0128 Coolant Temperature Below Thermostat Regulating Temperature

 

You can get an OEM or a Dorman which is equal in quality. Even colder id get it addressed as soon as you can.

 

Are we talking an SXT here? Fan settings in tune are slightly different.

As for thermostat the hemis use a 203F but just noticed this in the 2015 Challenger FSM.

What I find interesting is my Durango V6 thermostat is stated as closing at 195F, yet the above 2015 challenger FSM says "all engines" (except the 6.2) have thermostats that close at 195F. Something is not right here?

2017 Durango FSM