As a Mechanical Engineer who has worked as a Product Planner at a major auto company in the past, has worked at a manufacturer of large jet engines, and also worked with motorcycles and cars for 40 years, I appreciate your googling skills.

But as much googling as you might do, you will not convince me one should use their engine at WOT immediately after starting when it is zero degrees outside. Engines do require a warm-up period before being operated at high-RPM and/or high load. A temperature gauge shows you when the engine is at normal operating temperature.

Note that warm-up, does NOT mean idling at a standstill.


P.S. A working temperature gauge also provides an indication of thermostat failure, a quite common problem. Without the temperature gauge, such a problem will go undiagnosed until the thermostat failure becomes dramatic.

P.P.S. If you park your diesel outside overnight, start it in the morning when the temperature is 5 degrees, drive it a mile to the Interstate, and then start driving on the interstate, do you know how long it takes for the engine to warm-up? I do, as I have been logging coolant temperature vs. time data via the OBD-II port over the past few thousand miles. Care to take a guess?