I am going this weekend to look at a 88 IH flatbed dump with 250k miles on the 466 engine. I have been looking for something with less miles but finding a good diesel with air brakes and decent dump for around 5k is tough. Anyway the owner says it runs great with no issues. What specifically should I be on the look out for as potential problems when I go look it over? Assuming it runs good with no smoke and the fluid all look good with no signs of contamination is there anything else to look for? It seems like the 466 either last for 300-500k miles or it needs a rebuild at 125k. I know its a gamble but I am just trying to find something that isn't going to need a $7k rebuild in the next 10k miles. The owner has only had it for about 8 months. He said he bought it with intentions of setting it up to tow his smaller grading equipment but he found a good deal on a different truck that was already set up for towing shortly after he bought this one. The owner who had it before that was a residential builder so I don't have any way of knowing any maintenance history.
The 466 is a good motor, not a whole lot of power but so long as its maintained it will run a long time. Find a way to drive the truck up a good hill and see how much it pulls. Flat ground will not give you much insight. If motor is good check the spring shackles and king pins, see if they are well greased and even if they will take grease. If they won't take grease then the maintenance was not done on a regular basis
Try to go when it's cold to see how it starts and idles cold, if it's hitting all cylinders evenly and smoothly. Then look at the blowby when it's warmed up, that's real subjective, but if it's blowing an oily mess that's a bad sign, and if you can barely see it that's good. Check underneath to see how much the seals are seeping, that's getting old for rubber seals to keep going. Clutch, brake and tire life also.