Originally Posted by m-chan68

Well the diesel mechanic isn't very familiar with the operation on these engines then. THIS issue is likely caused by a high pressure oil system leak. These engines use high pressure engine oil to control fuel pressure at the combustion chambers. When the engine is cold, the oil thickens up enough to overcome the leak source to enable the engine to start. But when the engine is at operating temperature, the oil thins out and can't produce enough pressure for the engine to start. Your STC fitting is likely needing to be ditched in favour of the updated one piece branch tube connector. The part number from Ford for this kit is 4C3Z-9B246-F.