Originally Posted by MyTruck
Can someone explain why a diesel engine will have issues when used in an unloaded condition. I have hard time understanding why it would be an issue. Isn't the weight of the truck itself considered a "load" already. Many vehicles in other countries use diesel as the main source of fuel for cars and trucks.
Sure not a problem.
What the vehicle is used for is how automakers size an engine (duh right). A diesel engine in a car is only required to carry the load of 4 passengers and some luggage. The difference between empty and fully loaded is a relatively narrow range. Maybe 500-600 pounds. Compare that to a heavy duty truck and the range is much wider. From 7K pounds empty to 25-30K fully loaded. The engine has to be built to handle the super heavy loads so the cooling systems are sized according to the high end of the tow rating.
Because the cooling systems are so efficient (and huge) on the heavy duty trucks, when unloaded, the cylinders never get hot enough to burn off all fuel. This causes fuel to contaminate the oil, removes oil film from cylinder walls, adds soot to the turbo and injector tips, and can cause issues with the emissions systems on modern trucks. Newer trucks have design features to help mitigate some of these issues but a diesel truck is most efficient when loaded.
This is also why you are seeing very small (relative) diesel motors in the new half ton trucks. They don't need to be as heavily loaded to work efficiently.
Hope that clears it up.