Another reason these engines may not maintain temp in the winter is because they have 4 valves per cylinder. I had my ISB Cummins for 10 years, and GDE never did a tune to it

Any ways, that is also a 4 valve per cylinder engine. In frigid temps that engine will be hot from a run, yet cool right down to the point that unburnt fuel is coming out the exhaust if it is allowed to idle for an extended time, the gauge will go to the cold side. This is due to the excessive air flow that goes with 4 valves per cylinder, plus its efficiency allows it to idle on very little fuel. Also keep in mind you charge air cooler becomes very efficient in colder weather.

_________________
2006 LTD Bright Silver loaded with all the needed mods, CCV intact.
Proudly supporting CRD vendors, and their development of quality parts and accessories.
Equipped with HDS thermostat, plenty of heat, faster warm-ups, increased fuel mileage.

Today had the Eco Jeep out in 10 deg temps. Went to bank drive through, noticed gauge was mid way in 1st left qtr. during extended idle, so I shut it down. So yes, like my 24 valve Cummins it will not maintain temp at idle. When I drove away, I turn OD off until the temp got near the 1/2 way mark. Put the OD back on, and the temp stayed almost 1/2 way. Any ways, I usually drive the Cummins in a lower gear as well for a quicker warm up. The little bit of fuel saved driving in the highest gear is not worth the unburned fuel in the CC oil. So let it rev, get the temp up, then shift to the high gears.

_________________
2006 LTD Bright Silver loaded with all the needed mods, CCV intact.
Proudly supporting CRD vendors, and their development of quality parts and accessories.
Equipped with HDS thermostat, plenty of heat, faster warm-ups, increased fuel mileage.