Damage to the fan clutch wire harness and / or erratic fan clutch operation can cause the engine cooling to not turn on. A new fan clutch assembly will be needed to fix this problem.Google+
Car Problem Reports
Ford E-350 Possible Engine Overheating, Cooling Fan Not Coming On - Diesel
Ford E-350 Problem
Engine Affected: 6.0L V8 Diesel Turbo
Visitor, 2006 Ford E-350, 6.0L V8 Diesel Turbo, 137,000 mi
noticed that my truck was overheating , opened the hood and founded that the harness wires from the fan clutch were hanging down and the other half were on the fan.The cost to replace the fan clutch $896.00 I think Ford should have had a recall on this. Or better secure the harness.