Billybob wrote:
You can pull out the relay for the viscous heater from the fuse/relay box (PDC) under the hood.
This let's the pulley run free.
It will post a CEL but try this out for a while to see if it makes a difference.
Thermostat installed facing in the right direction?
I have never worked in this area so I do not know if doing this would make it run hotter or cooler.

It is impossible to install the thermostat in the wrong direction as it is in it's own housing.
xsfpns: You could be dealing with more than one problem. One thing I can tell you is that it is highly unlikely that the viscous heater is the problem. I also do not think that the modifications to the EGR system are to blame, either.
WWDiesel makes a good point; and I will elaborate on what he wrote. There is an issue from time to time with the O.E. temperature sending unit. To eliminate that possibility, please get an actual temperature reading in degrees using an OBDII reader or a Torque Pro app with your mobile device. Cross-reference that temperature reading with a reading from an infrared temperature gun pointed st the top of your thermostat. These two readings should be the same or within a couple of degrees of each other. If they are significantly different, (10 degrees or more), then it is likely that your O.E. temperature sending unit is malfunctioning and must be replaced. This test assumes that the IR gun is functioning accurately.
DO NOT trust the O.E. temperature gauge. It is neither accurate or linear.
You have the classic signs of a failed thermostat, but even a new thermostat does not operate the engine at a high enough temperature. The rest of the world gets a 195 degree Fahrenheit thermostat; all North American Liberty CRD vehicles get a ridiculously low 176 degree Fahrenheit to meet the Environmental Protection Agency's NOx pollution control standards. This is the crux of the problem with CRD engines running too cool; the quality of the O.E. thermostat that fails too often is also a major contributing factor.