No intention to high jack Paddy's awesome thread..but.. I have to disagree with alot of what you're saying, Tim... It is indeed true that diesels will run a lot colder in colder ambient Temps when not under heavy loads... Much heavier and thicker block, bigger rods, bigger cams, bigger intake/more air, more oil, more coolant, generally no throttle body.. All of it does add up and makes it much harder for a diesel to maintain the ~200f temps that it so adores.. I do agree with tighter tolerances, friction, combustion, but it's on such a different scale. Idling temp comparison diesel to gas is a world of difference. In 10degree ambient temps, it will take ~35 minutes for a diesel to reach ~130f ECT, even at high idle. In negative temps, unless you're pushing higher rpms(let's not split i6 and v8 diesels here), you won't see 200f ECT for long. Cruising at lower speeds and rpms you will be lucky to float around 180 and never open the t-stat.... The block stays MUCH cooler than a gas ICE at this range, which is why it is recommended to have a grille cover if you want above 65f heat from the core...
Also... If you're seeing 1500f EGTs in your diesel regularly and you're not flowing 100mm3 through that injection pump, you might want to downshift or lock out overdrive... 😆🤯