Some really good guidance was offered by bismic
I would recommend trying for a 2006 year model. I think that buying a used 6.0L may be one of the best deals going right now. A lot of people have heard the horror stories and have traded them in. If you find a good price (which I have seen quite a few good deals) AND you have checked into the reputation of a local dealership on repairing the 6.0L - then GO FOR IT! So much depends on having a dealership that has competent techs to troubleshoot and work on any future problems.
If you are looking at used 6.0's here are a few considerations (along w/ the OASIS and CARFAX reports that are essential).
Some 6.0L weak points (things to check):
Look for signs of coolant degas bottle overflow (dry white residue on and around the degas bottle or no level in degas bottle).
Lots of idling can cause EGR problems. I look at the hours on the engine (if it has this monitored) and divide the miles by the hours (is it below 30? If so, may have had lots of idling).
Even without much extended idling EGR valves can plug quickly - maybe negotiate for a new EGR valve. In fact, I would negotiate for them to pull the EGR valve to inspect it (have them show it to you when it is out and then you need to look into the intake). Check for wetness (w/ rear end jacked up) and for excess soot. Wetness indicates an EGR cooler leak. If the valve is gunked up, have them replace the valve. If the intake is real bad, you may push them to clean it as well.
Look underneath for oil leaks - some trucks have had a lot of them.
If you buy from a dealership, I would negotiate for them to install the latest flash of all 3 processors (PCM, FICM, ECM).
Negotiating for an extended warranty is always a good thing as well.
Try to find out about the routine maintenance:
· Filter change intervals on time? What kind of oil (CI 4 + or CJ 4 - one of these is required)?
· OEM filters? Look at them and see what kind they are. Aftermarket filters can cause MAJOR problems.
· Find proof of Transmission being flushed/changed - it is recommended every 30,000 miles.
· Any exhaust problems visible (i.e. lots of white or blue smoke)? White smoke may mean an EGR cooler leak.
Check for any FLUID leaks (as stated previously - LOOK SPECIFICALLY FOR OIL LEAKS - 6.0L are prone to many of these from many possible places!!).
CEL (Check Engine Light) on? Consider getting a code reader and check for DTC's. You can have active DTC’s without a CEL.
The Electronic Shift on the Fly ESOF sometimes fails due to vacuum leaks. Be sure to check this out (several times in and out of 4WD and/or take front wheels off to inspect).
Check for excessive wheel bearing wear (looseness), sway bar (end link looseness), or ball joint looseness. Ball joints and sway bar end links tend to go out in the 70k-90k range. Jack one side up at a time and see if each wheel moves top to bottom only, if so, it is the ball joints. If it moves in all directions then probably wheel bearings.
Check the coolant - it should have the Motorcraft Gold Coolant - anything else and there may be problems. Look in the "degas" bottle and inspect the fluid - it should be gold colored and there should be NO OIL visible (oil emulsified in water can show up as brown sludge). As previously stated, the degas bottle should not have white residue around the sides of it (possible overheating issues).
Any evidence of a tuner ( aftermarket air filter, gauges, etc)? Tuners may or may not be bad. Some tuners are MURDER on the transmission. Some dealerships will cause you a lot of problems w/ them - even if you bought it that way used.
Aftermarket air systems could be a problem. Many of them (like K&N) do not filter as well and could cause issues. Up to 500 hp, the stock air system is best!
Try to find out if the original owner ever ran it empty on fuel or have plugged filters (fuel pressure below 45 psig can damage injectors)?
Then the common stuff I'm sure you know:
· Look at and smell the fluids. Make sure fluids not burnt, not too thick or dirty.
· Check the tires - abnormal wear?
· How do the brakes look? Any pads need replacement? Are the rear brakes excessively worn?
· All electronics working? Especially the AC (repair can be expensive)?
· Dents? Air bag been replaced, etc.
· See if he has any repair or maintenance records.
· Take off the price for windshield dings, paint chipped, torn upholstery, etc.
· Does the truck look too clean? Does it look like the oil was just changed? May be hiding something.
· Any extras - tool boxes, bumpers, etc.?
· Drive it - does it hesitate, stutter, or surge? Does it blow white or black smoke? When driving, brake fairly hard - note any pulls, pops, clunks, rattles, etc. How does it accelerate? You should romp on it pretty good. Drive in reverse and then back and forth - listen for clunks.
Add or subtract value based on condition, high miles, and presence of extras.
A lot of duplicate information I unknowingly offered in the same thread:
Basic things to check when you go to look at a 6.0........for starters, make sure the truck is cold when you show up. Once the truck is up to temp, a lot of issues can be easy to hide. I won't touch on the REALLY basic stuff, like checking for oil leaks, but here's what I'd recommend:
1. Look in the degas bottle and see if the coolant appears to have layers (sign of oil or diesel in the coolant). Also look for sediment and debris in the degas bottle. This may be an indictor that the oil cooler is clogged or clogging.
2. Smell the degas bottle cap. If it smells like diesel, the truck likely has a cracked head (or heads)
3. Look for white residue on the top of the degas bottle and on the underside of the engine hood (driver side, above the degas bottle). If there's a white residue in either location, there's a good chance the head gaskets are blown
4. Start the truck. Again, make sure you're starting a COLD engine. If the truck idles rough then smoothes out, there are injector(s) suffering from stiction. If it doesn't smooth out, there's probably some bad injectors. Either way, you'll have to consider replacing them sometime in the future.
5. Try to watch the exhaust when you first start it. Is it white, bluish-white, or grey? If there's any smoke, it should be black.
6. If you have the capability of bringing along a ScanGauge II or other monitoring device, do it and take the truck for a test drive. Run 60-65 mph for 10-15 min AFTER the truck is warmed up and look at the coolant temp and the oil temp. If they're more than 15* apart, the oil cooler is clogged and will need to be replaced.
7. Taking a step back, use the monitoring device to check FICM power. If it's less than 47v key on/engine off, when cranking, or when running....well, the FICM will need to be replaced.
8. Pull the air cleaner off and look for dust and dirt in the tube. If it's not 100% clean, try to get your eyes on the turbo inlet. Check the turbo blades and around the turbo blades on the housing for wear.
9. You can also use the ScanGauge II or other device to pull codes. Print out a list of the codes before you go so you know what they mean.
10. During the drive, roll into the throttle when the truck is in top gear with the torque converter locked. Watch the exhaust. If there's smoke, the turbo vanes may be sticking. The truck shouldn't buck, surge, or smoke.
11. If the truck has cruise control and/or radio control buttons on the steering wheel, check to make sure all of them work (clock spring failure is farily common)
12. Check the firewall for any soot, and listen for any odd whistling when the truck is running and being driven. The flex sections of the Y-pipes are prone to cracking and causing exhaust leaks.
If all of these appear to be okay, STILL take it to a reputable diesel mechanic who knows the 6.0 before you buy it.
To add to the 4x4 check -- shift it into 4wd. Does it work? Turn the A/C on and see if it blows through the defroster vents? If it does, you probably have a vacuum leak and troubleshooting it can be a huge (and expensive) PITA.