The 6.4 does not typically "self destruct", in many cases it is aided in destructing by operator who do not understand the requirements of the new emissions controlled diesels and use them for the wrong type of service, neglect maintenance, etc. Properly operated and maintained the 6.4 and other emissions controlled diesels do just fine.
Now if you are looking at a used one, you have to be concerned about it's useage and maintenance prior to your purchase. Unlike pre-emissions diesels the post-emissions diesels can go bad very quickly if they are neglected or are used for all short trips.
The problem with assessing a used post-emissions diesel is that much of what you want to inspect is not readily visible. On the 6.4 you would ideally want to inspect the following:
- Lower HFCM fuel filter and housing for signs of gunk buildup, and to ensure the filters have been changed.
- Upper fuel filter, looking in the bottom of the housing for signs of rust spots or metal flakes both of which can mean expensive fuel system repairs.
- The water pump back housing for signs of cavitation damage.
- Coolant nitrite test to see if the coolant has been maintained properly.
- Used oil analysis on a sample with ~5k miles on it.
- Check for signs of leaks at the radiator hose connections and the radiator itself.
Since a used vehicle at a dealer has probably recieved a basic service with new oil and filters, some of the information you want will not be available at all.
Clearly the water pump housing can not be inspected in any reasonable fashion. The lower HFCM filter and housing can't be inspected without draining a quart plus of fuel and making a mess so it's not easily inspected.
The upper fuel filter can be inspected fairly easily with a flashlight, wrench and a container to rest the filter in when removed. This is one inspection you should absolutely do since a high pressure fuel pump and injectors is a good $8k repair.
The coolant nitrite test is another quick and easy test you can do, clip a test strip on the end of a long hemostat and just dunk it in the coolant degas tank, wait the 45 seconds and compare the color chart. Most dealers probably won't change the coolant on a used truck so it your nitrite test shows under 300ppm nitrite, reject the truck for neglected maintenance.
My standard maintenance recommendations for the 6.4:
If you have not owned one of the newer emissions controlled diesels previously (any brand), be aware that they are far more dependent on proper maintenance than earlier diesels.
Key 6.4 maintenance items:
* Oil changes every 5,000 miles, with quality oil (synthetic recommended), used oil analysis (Blackstone) for every change. Use only Motorcraft oil filters or the Racor (OEM) equivalent.
* Fuel filter changes every 10,000 miles. Use only Motorcraft FD4617 or the Racor (OEM) equivalent filters.
* Coolant nitrite testing at least every 15,000 miles. I recommend every 5,000 miles at the same time you do the oil change for simplicity, the test strips are inexpensive. Do not be confused by the test directions warning not to sample from an overflow tank, the 6.4 does not have an overflow tank it has a degas bottle. The degas bottle is part of the coolant loop with constant circulation so it is a valid testing point. I do not bother "taking a sample", I simply clip the test strip on the end of a long hemostat and dunk it in the degas bottle to test. If the test is below 800ppm and above 300ppm add two bottles of VC-8 additive. If below 300ppm the entire coolant system must be flushed with VC-9 cleaner, rinsed well and refilled with new coolant.
* Cooling system flush with VC-9 and refill with Ford Gold coolant every 60,000 miles, sooner if you have neglected testing and the nitrite is under 300ppm.
* Use a quality fuel conditioner such as the Ford PM-22a/23a conditioners at every fueling. They add lubricity to the fuel, something that ULSD is lacking in which helps protect the high pressure (up to 26,000 PSI) fuel pump. They also help to reduce soot production which results in less frequent DPF regens and less fuel dilution in the engine oil.
* Drain the HFCM water separator monthly. The fuel drained can be poured back into the tank carefully leaving behind any water at the bottom of the collection jar (normally very little). If the water separator drain does not flow well or at all, it may be clogged with either parafin blobs or with bacterial growth. In either case at a minimum the drain valve cover needs to be removed and the clog cleared. If the clog is significant the HFCM cover needs to be removed for full cleaning. If the clog is white and waxy it's parafin and not a significant issue. If the clog is brown or similar and more slimy it is bacterial growth and the fuel tank should be "shocked" with a biocide such as Power Service Bio-Kleen which should not be confused with their Diesel-Kleen.
* The truck should not be used for all short trips and stop and go traffic. The 6.4 and other emissions controlled diesels need regular longer periods at highway speeds to allow proper DPF regeneration and to get to proper operating temperature to help reduce fuel contamination in the engine oil.
* The latest PCM flash (11B23) does not provide continuous indication of when a DPF regen is taking place, it does however add much improved engine monitoring for developing issues. Over time you will get to recognize the subtle changes, but I recommend adding something like the ScanGauge II which will allow you to monitor the DPF temperature which is a clear indication that a regen is in progress when over ~600F.
* Avoid shutting the truck down with a regen in progress. If you have to, run the engine at high idle for a few minutes in park before shutting down to allow the turbos to cool down to normal temperatures before shutdown. If you are interrupting the regens you will see it in your Blackstone report, otherwise you should see very little fuel dilution, <1%.
You should also absolutely get the Ford ESP extended warranty, any repairs to the 6.4 are expensive and a single big repair can easily cover the cost of the ESP warranty. The coolant nitrite testing that many people overlook *is* in the owner's manual diesel supplement, so if you neglect it Ford can deny warranty coverage for resulting damage.
Other Super Duty maintenance items:
* Batteries - The batteries in these trucks are not the maintanence free / unmaintainable type, pop the caps to check and top up with distilled water periodically.
* Change transfer case fluid every 60,000 miles.
* Change rear differential fluid every 50,000 miles on DANA axles (F350 DRW and up).
* Change transmission fluid and filter every 60,000 miles on Torqshift transmissions (100k on manual transmissions). If you have the early Torqshift with the external filter the interval is much shorter.
Coolant test strips - Buy the 4pk, not the bottle of 50, the strips have expiration dates and you'll only need <10 per year. Most dealer parts counters should have the test strips, NAPA has them, or order direct from Acustrip.
Used oil testing - Blackstone Labs, get the pre-paid 6pk of test kits to save a few bucks. You don't need the TBN option:
Ford ESP extended warrantys - You can buy them online from real dealers, or use the online price from a real dealer to negotiate a better price from your local dealer. You absolutely want the ESP, while the 6.4 is not problematic as some claim as long as you maintain it properly, nearly any repair is big $ and one good one will cover the ESP cost:
Ford Extended Warranty - Genuine Ford ESP
DPF, oil, coolant temp monitoring - ScangaugeII, you will need to program the X-gauge commands for the 6.4:
ScanGauge - Trip Computer + Digitial Gauges + ScanTools
Ford Specific XGauges : Linear Logic : Home of the ScanGauge