Originally Posted by 444 ci
oil pan rust, blow by,oil in the coolent or coolent or diesel fuel in the oil
Also check for leaks around the High pressure oil pump lines the o rings tend to go bad, also check for leaks around the turbo pedestal, check for leaks around the rear main, check for trans slippage if its 4r100 check the clutch out if its zf6, and check the ball joints, make sure the 4wd works,check for white smoke during a cold start that is a sign of bad gpr or glow plugs or both, check the alternator out meaning look at the battery amperage when you cold start it-it shouldn't fluctuate. Basically it don't be afraid of a lot of owners if it's a good deal these trucks truly are tough as it gets.
Mine gets 13mpg and diesel is more expensive to fill up and maintain these trucks are not cheap and should never be neglected with maintenance so if you truly don't plan on towing you don't need it unless you love them and have $ to burn, have fun!