Originally Posted by MyTruck
If the coolant temp gauge reaches operating temp which is about 185-190 deg, this tells me the engine is at working temp range. Loaded or unloaded, the engine is working at the designed range in terms of temperature. If the truck is loaded, the coolant temp would rise but settle back down. So if the coolant temp gauge is used as a measurement of efficiency, then I don't see how loaded and unloaded conditions would affect the decision whether to buy diesel or gas.
Cylinder temperatures and water temperatures are very different. You can have stable water temps but have the EGTs vary greatly. It is the high cylinder temperature produced by heavy loading that burns off the soot on the injectors and turbo and helps burn the fuel more completely. Efficiency for the sake of my argument basically getting the most energy from the fuel. This can only be done if all the fuel is burned in the cylinder.
It's not going to kill an engine in 50K miles if you never put a huge trailer on the truck but it is just something to keep in mind if you want to go 200-300K miles and have a healthy engine/injectors.