[enter.sandman5591]

2011 6.2 S.crew This started about 2-3 weeks ago. It would seem that the temp gauge isn't getting much above C while driving. We've had some pretty cold days here the past few weeks, anywhere from 15-30 degrees F, however that's never been a problem in the past 8 years I've been driving the truck. It's taking much long than usual to reach normal temp while at idle, and once I'm moving the gauge drops like a stone. Average commute is about 20-25 mins, all highway. The cab heater also doesn't seem to be working well either. Set at max, the air coming from the vents barely gets warm.

I checked the coolant levels, there all good, no leaks that I can see and it's still bright orange. My first guess is the thermostat is stuck open. Or I'm just underestimating the effects the cold weather is having on a 10 year old truck with 140,000 miles.

Any thoughts..?

 

[guardrail]

I would say the thermostat is stuck open.
When the truck is cold, look in the radiator and see if the antifreeze is flowing

 

[AMG Ducati]

I had a similar situation about a month ago and also got a code which said something to the effect of:
"The coolant temperature is below normal operating temperature." Sorry I don't remember it exactly and I don't have the code anymore. I assumed it was the thermostat sticking and like "Guardrail" above said, I checked the antifreeze flow to verify that. The code also listed a couple other suspect possibilities: "fan clutch not working," which is easy to check, and "Temp sensor bad," which was obviously working as I had temp indication.
I was about to change the thermostat the next week and all of a sudden, the code went away. I noticed that while it was throwing a code ("CK ENGINE" warning annunciator on dash illuminated), the keyless entry would not work but started working again once the warning went away.

 

[enter.sandman5591]

Thanks for the feedback, I will be checking the radiator tomorrow morning. Honestly, I'm surprised the truck hasn't thrown a code yet, I keep expecting one to pop up on the dash, although I've been using it sparingly since this issue started.

The only other thing I can think of as a cause would be air in the system, I'll be checking for that as well.

 

[AMG Ducati]

Yeah, I got the "CK ENGINE" light so I checked for a code and found that one. But it's gone away and I haven't seen it back, knock on wood. If it does, I'm just going to change the thermostat, in fact I may just do it anyway. Hope that's all it is for you.