Engine starts good when cold. After driving and trying to start,cranks over but will not start.2006 f 250 6 liter

On diesel engines that will not restart, after they are warmed up, it's often a sign of a tired fuel pump. As they heat soak, inside pump head clearances increase and it will no longer develop sufficient fuel pressure at cranking speed. While it's running, fuel helps cool the pump by carrying the heat away. If this sounds like your situation, install a new Motorcraft fuel pump and under frame fuel filter.