Diesel, I had a 345k truck I sold several years ago with never a problem and it was running good when sold, its still local and the guy put an injection pump on it after another 60k on it and its still going, take car of it with good oil and changes and keep a eye on everything. No reason you can't get 400k easy out of these motors. They are not the most powerful things when it comes to towing when comparing to todays present diesel truck market but they do a good job regaurdless. If you drove it you would think it had 50k on it, just broke in. Just my .02 worth