Our engines nowadays are built around the ULSD 15 ppm sulfur mandate. We, as the end user at the fuel pump, don’t need to be chemists, or have to complete the refining process by adding snake oils and elixirs in order for the engine to run properly.
Step away from the Kool Aid, it is blocking sound thinking.
The Bosch injection systems are built around using better fuel, both composition and cleanliness, than we have in this country. Period. End of story. You do not have to be a chemist to understand that fuel QUALITY is something completely different than a ULSD 15 PPM EPA mandate. The cracking process to remove the sulphur components does NOT guarantee that when the fuel is pumped into the vehicle tank it meets minimum spec. There is a LOT of steps and handling between the refinery and tank that can and do introduce contaminants, both solid and liquid.
Really though, the key reason for running an additive package is the cleaner components. The new trucks now have adequate filtration for water and solids for the most part but they cannot filter all of the sub-micron asphaltenes that are causing the issues with injector fouling. If one is following the issues it is obvious that this a major part of the inejction system failures and is really inherent to the ULSD and CR fuel systems with the constant fuel heating and cooling that happens. Asphaltenes are tar that is being cooked out the fuel due the cracking process that has broken the long change molecules and aromatics in dciesle down to remove the sulphur component, it is the black stuff on the fuel filter.
Tar build in the clearances in a CR injector just guarantees the internals get scored and start to fail. It is also partially responsible for the carbon buildup on nozzles that raise havoc in-cylinder. An additive package not only needs to provide better lubrication that the refiners can ever add back, but, it also needs to provide a solvent to break up deposits in the fuel system and cylinder. Without those additives I see a lot of 6.7 engines prematurely fail from washed cylinders, melted pistons, head gaskets of course, and actually burning the tips off the nozzles.
If you have an injector that is having problems from build up it is pretty easy to test by a high does of cleaner and additives to see if it will break loose and work correctly. However, even if it does it is compromised and th eonyl fix is rpelacemnt. Already replaced 3 injectors on a sub 200k 6.7 due to failures and the other 3 are done also. Running a strong additive package fixed the worst one a 4k mile trip and at least got it stop hammering the crap out of the clutch and transmission but it is still flaky depending on fuel.
Bottom line, not running additives and\or an injector cleaning periodically if you do a lot DD is just a recipe for an engine melt down. The truck shops and machine shops I periodically work with have a LOT of engines with all these problems going thru there all the time. The proof is out there if one cares to track it down.