Thanks for the added info guys. Yes, common rail injection has provided dramatic improvements in diesel efficiency. Only downside is that these common rail systems are a little more sensitive/finnicky, but careful attention to fuel quality and filtration takes care of most of that. Although I still have concerns about this ULSD and its possible negative effects (shortening their life) on these injectors.
Anyway, my concern is based on two things: 1) Oil analysis from Blackstone Labs. I had a test done on an oil interval that was all unloaded commuting and compared against oil analysis from running loaded and dilution was up substantially on the unloaded interval (something like 3% running unloaded vs less than 1% loaded). It was a few years ago so I'll need to see if I can dig up the reports to give you exact numbers. 2) Personal observation. After running light unloaded for some time, the truck's performance becomes quite sluggish. Then when I hook up some weight behind it and run it hard for a while, then unhook, it has all its power and economy back again. It seems to respond well to the old "Italian tuneup," in a sense, to clear it out and clear the unburnt fuel. Also, after loafing along for a while and then getting on it, it blows quite a bit of smoke for the first couple WOT runs until that unburnt fuel is burned out of there. You guys with the newer 6.7's may not notice this much, but the old 5.9's do it. Anyway, while the common rail injection system is dramatically improved vs the older mechanical injection, I do still tend to believe they don't quite run optimally at very light loads. It's probably not quite achieving complete combustion of all the fuel at very light load, but that's just my guess from what I've personally observed. Anyway, maybe there's more to the story that I don't know, but based on what I've learned and research so far, this is what appears to me to be going on with these CTD's. Despite this, I still love my truck and they'll have to peel my cold dead hands from the steering wheel to get me to part with it.
