Although it is a reasonably cold day here today (-28C on drive in), this issue has been happening since it cooled off a bit this fall just not as pronounced.

When I start my truck and leave the garage, my temp is about 37-40C (Heated Garage, Forscan enabled numbers above gauges). It will gradually climb but then due to my hilly backroad drive in, will actually start to fall when off the gas and coasting down a hill

This morning, I saw it go to 69 and drop to 60 at one point and after a longish hill climb and then stopped at a light once I got to town, it went from 85 down to 71. Enough that even without the digital readout, I could see the gauge drop. This morning it did not get up to or past 90C which it usually does. This is on a 25km commute.

In the summer, it seems to go to 95C +/- and stay there - this is how I have always seemed to experience what I believe is the correct operation of a thermostat. With the active shutters, I would think maintaining this would be easier. In my '16, I did not have or experience this issue. The dodge rental I had last week for a business trip (also has digital readout) went to 94C and stayed put until I shut it off.

Is my thermostat bad? Any other ideas?

 

I would verify actual coolant temp with a dedicated gauge, if you're really concerned about it.

And the grill shutters are for aero improvement (ie: FE), and have little effect on engine operating temp's.

 

I haven't seen anything like this on a modern vehicle, but years back it was common to see one temperature drop, perhaps 2, when the thermostat opens for the first time. All the cool water begins circulating through the motor more quickly, temp gauge would show the result. It could happen a 2nd time, but by then the coolant is fairly stable and thermostat is working smoothly.

I'd suggest to just continue monitoring. If it continues just as you mention here I wouldn't be too concerned. If the results are less stable or with greater swing in temperature, perhaps something is going on.

Is the coolant filled to the correct level?

 

It is all filled up to the appropriate level for sure. I will keep an eye on it and maybe throw a new t-stat in if it continues.

 

Keep in mind this is a fairly small engine and it's not making a ton of heat, especially if you're driving easy. To maintain temp at -30C you may need to cover portions of the grille.

 

I thought about that but portions of the grille are covered by the shutters. That and the 3.5 in my '16 (not H.O.) had no issue in colder temps. Went out for lunch and was watching it closely. On the gas, it builds temp, off the gas it drops. It is not like thermostat opens and it goes down, more like it may be stuck in the open position. Seems not right to me.

 

Watch the fuel economy screen while coasting. You will see that the fuel injectors shut off. Without any burn, you lose heat...especially on a small aluminium engine. Normal, but only noticeable at cold temps. Mine does the same. Below -30C here lately and it’s really noticeable.

 

It warmed up here today and was -22°C. I was out and about and idled for quite some time while my wife was in the doctor's office. Engine coolant temp never dropped below 88°C and peaked at 94°C. I'd say you either have a bad thermostat or bad engine coolant temperature sensor

 

I would tend to agree. May pick up a stat this week and pop it in on the weekend. Looks fairly simple after removing a bot of the turbo piping.

 

So I changed out the Thermostat and seal last weekend and have been driving around and although it may be slightly better, the problem still persists where it takes a long time to get hot and cools when coasting. The thermostat that was in there was not failed in the open position.

I am thinking the only thing it could be is an air pocket??? I am unsure of the best way to get this out. Maybe a vacuum tool???

I have heat in the cab and I don't think there is anything else controlling coolant flow.

Any opinions would be appreciated.