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The 6.4L Power Stroke's signature failure is its radiator: the diesel's radiator cracks and leaks coolant, commonly within the first 60,000-100,000 miles. Leaking or cracked radiators recur throughout the 2008-2010 Super Duty diesel complaint texts, several reporting a coolant puddle before 40,000 miles. Because the 6.4L is already thermally stressed by its emissions system, unaddressed coolant loss risks overheating -- and a replacement radiator is a several-hundred-dollar-plus job that many of these trucks have needed more than once.

Check — Look for coolant weeping at the radiator end tanks or a low/empty degas bottle with no obvious external leak; ask whether the radiator has already been replaced (a common repair on these trucks) and with what part.

The 6.4L's emissions aftertreatment is a chronic weak point. Recall 07V139000 (2007, MY2008 6.4L trucks) addressed excess hydrocarbons that can drive diesel-particulate-filter (DPF) temperatures too high during regeneration; the fix was a powertrain-control-module reprogram, and Ford listed the consequences as power loss, rough running, white smoke, and even a visible flame from the tailpipe. The same regeneration/DPF pattern runs through the 2008-2010 diesel complaint texts -- forced regens, "STOP SAFELY NOW" shutdowns, limp mode, and white smoke -- and the frequent regeneration also explains the engine's notoriously poor fuel economy.

Check — Confirm recall 07V139000 shows complete on the VIN; on the test drive watch for a regeneration in progress, warning messages, or white exhaust smoke, and ask about DPF/EGR service history and the truck's typical fuel economy.