It seems to me when you start discussing diesel longevity and cost of operation, you almost need to split it into two categories. I guess the best way would be to label them for me is pre and post-EPA modern regulations.
Pre-EPA there were no particulate filters or big EGR systems, diesel engines didn't have such sophisticated fueling systems, and there was still sulfur in the diesel to lubricate cylinder walls, fuel pumps and injectors. A diesel engine was relatively low tech and could run very simply for a long time. The stock 1996 f-350 7.3L Ford in our family has 294K miles on it right now and the list of engine repairs on it has been pretty small. One water pump, one alternator, one or two sets of glow plugs, two cam position sensors, an exhaust manifold leak, and I think it just recently got a fuel pump. Maintenance has been regular oil changes at 3500-4000 miles, a new fuel filter about once a year, and Stanadyne fuel conditioner at every fill up (especially once low sulfur diesel came about). This pickup has pretty much been operated like the stereotypical "how a diesel should be run." Always let it warm up, majority highway miles split between unloaded family trips and a lot of trailer towing, let it idle at the gas station or when running in to grab something from the store quick, and always let the turbo cool down for a minute or two before shutting it down when you come off the highway. Truck shows no sign of weakness or slowing down yet and still pulls a 40' enclosed gooseneck as well as it always has. I've observed others with the same kind of truck that drive them in short runs and on/off that do not run nearly so well anymore. Just my observations. This truck will not come all the way up to operating temperature unless you get out on the road with it (after letting it idle for a few minutes of course and then ease into it). Operates much more like a semi-truck so to speak.
The 2008 F-450 6.4L we have is a much different animal. Has, or did have, all the things listed above that the ol' 7.3L doesn't. Prior to deleting the EGR system, the oil in the engine was black as coal after 2000 miles and the intake was absolutely full of oily, black soot comparable to sludge buildup inside of a motor. The same was true on my friends 2012 Ram Cummins when we deleted it. I have a hard time believing that you are going to get 300k miles out of these newer engines running the manufacturers recommended 10k oil change intervals and breathing their own soot. Fuel filter changes every 10k miles and clean fuel are a must to avoid problems down the road. Fuel filters for a 6.4L run $90 retail at Napa. Also, if you are driving around and the regeneration cycle kicks in you are supposed to keep driving until it has finished burning out the DPF filter. The more stop/go in town driving the more frequent I noticed it needs to go through it's regeneration cycle. Plug one up and you will get one of those large diesel repair bills at the shop. Not sure if the newer trucks using urea are better for this or not. Only 80k miles on this truck now so can't speak to long term durability yet, but it's getting the same duties and treatments that the 7.3L did so we'll see in a few years.
The newer engines warm up far quicker than older diesels. Not quite as fast as my 2003 f-150 gasser, but almost. The H&S tuner that is in the 6.4L indicates that the oil temperature follows the coolant temperature pretty closely. It has also revealed that the temperature gage on the dash is only good for telling you when the truck has reached optimum temperature. It doesn't even start to move until the coolant has reached 120 degrees. From 170-220 it sits right in the middle. The quicker warm up times tell me that condensation and short runs on the newer diesel engines probably are not much worse than on a gas motor as far as straight temperature is concerned. That being said I still let my gas engines warm up a bit before I take off in them too. However, startup wear is still a concern IMO if you plan to go hundreds of thousands of miles. This is an exaggerated example of course, but something to think about: large caterpillar engines in a natural gas generating plant have an electric oil pump that kicks on for 60seconds prior to startup. Reason being the crankshafts are so heavy that they literally squish the oil film out of the main bearings. The oil pump needs to pressure up and float the crank on a film of oil prior to turning over or it will spin the main bearings right out of them. Diesel engines are built heavier than gas engines and I'd think the same principle applies on a micro scale. The fewer times you shut down or start an engine the better it is for it and the benefit goes up as you go up in engine size. Diesels also run much higher compression than gas motors so the startup wear is accelerated jus due to the shear pounding the combustion is putting on the components until the oil pressure is there.
In summary it is my belief that if you want a diesel motor to last and run as good at 200k+ miles as it did when new then feed it clean air and oil, keep up on fuel system maintenance, let it warm up some before operating, let it cool down some before shutting it down, put it to work, and don't short run it.
For a gas comparison sake, my 2003 f-150 with a 5.4 has 283k miles on it now and has had several sets of spark plugs and boots, one set of coil packs, a couple alternators, had a head gasket blow out at 260k miles, and timing chains, tensioners, and slides done at the same time as the heads were off for the gasket. Now has a check engine light that doesn't want to go away. This truck has seen a lot of highway miles between me and the previous owner, but also sees a lot of in-town stop and go driving now. Oil gets changed every 3-4000 miles on full synthetic oil. Oil changes and fuel filters are much cheaper on this rig for sure, but repairs have actually been more costly than what the diesels have been running us. It did cost $3k to get the EPA parts off of the 6.4L though. And if the cab ever has to come off for a major repair on that it will be $$$. The f-150 does good with a 2 place trailer and two sleds or two quads. Any more than that and you are working it more than I like to. And it really wheezes for air over the pass going into Cooke City. I know new 1/2 tons are much more capable than my old one and the ecoboost shouldn't have the power problem at elevation. It is no where nearly as stable or surefooted on windy or slick roads either, but we all know that.
I know a lot of people don't have the means to have two pickups, but right now I'm keeping my f-150 for in town driving until it dies someday and keeping the diesel parked for road trips. I understand the creature comforts in a new truck are hard to resist having and using on a daily basis too. Especially when you are writing a check for a truck that sits 20/30 days of the month.
