Failure mode - Ford 6.7L Power Stroke Diesel (Scorpion)

Dual-circuit cooling system leaks (radiator / crossover tube / degas bottle / water pump)

Reliability tier: verified - verify before ordering, see /disclosure/

Symptoms

low coolant warnings or a slowly dropping degas-bottle level with no visible puddle (small end-tank seeps often evaporate on hot surfaces)
sweet coolant smell after a drive, or white crust/dye staining along the radiator tanks and crossover tube
rising coolant temperature while towing grades (points to a clogged/airbound system, not just a leak)
elevated charge-air and transmission temperatures without a corresponding engine-temp spike - a SECONDARY circuit problem, easy to miss because the primary gauge looks normal
water pump weep or bearing growl, most common past 120,000 miles

Compare with the other causes of the same sign on this engine: losing coolant (2 causes) · overheating or temperature creeping up · ticking, knocking, rattle or whine (3 causes)

Root cause

The 6.7L uses a dual-circuit architecture: a primary circuit for the engine and a separate secondary low-temperature circuit serving the air-to-water intercooler, transmission cooler, and fuel cooler (its own pump, thermostat, and degas bottle). This keeps intake air dense and driveline temps controlled but doubles the hardware that can leak. Common leak points: primary radiator plastic end-tank crimps to the aluminum core, the coolant crossover tube seals at the front of the engine valley, degas bottle caps that fail to hold pressure, and water-pump weep holes as the pump ages. Gen1/gen2 (2011-2019) trucks are the most affected per an aftermarket parts maker's 6.7L Power Stroke guide; Ford revised radiator construction over the years, but plastic end tanks under ~16psi of hot pressurized coolant remain a wear item on any high-mileage truck regardless of generation.

Diagnosis

a pressure tester and UV dye find nearly every leak on this platform - diagnosis is conventional
check BOTH circuits - the secondary bottle is routinely ignored until it causes downstream symptoms (charge-air/trans-temp creep) nobody connects back to coolant
treat repeated coolant loss seriously rather than topping off for months: chronic low secondary coolant cooks the intercooler (feeds Intercooler condensation ingestion + cold-side charge-pipe fatigue); chronic low primary coolant risks head-gasket damage on an engine that is otherwise unusually resistant to it (contrast this project's 6.0/6.4 head-gasket narrative, which does not transfer to the 6.7L's 6-head-bolt design)

Fixes

replace the radiator; do hoses, cap, and thermostat(s) in the same job on a truck past 100,000 miles ()

radiator - more than one option: 6.7L Power Stroke Main Radiator (Rear position), 6.7L Power Stroke Main Radiator (Rear position) (current service PN BC3Z-8005-K), 6.7L Power Stroke Main Radiator, XDP X-TRA Cool XD291 (2011-2016)
ford-powerstroke-6_7: coolant-hose (honest catalog gap)
thermostat - more than one option: 6.7L Power Stroke Thermostat, Driver Side, 6.7L Power Stroke Thermostat, Passenger Side

replace the coolant crossover tube seals ()

coolant-crossover-tube - more than one option: 6.7L Power Stroke Coolant Crossover Tube (Ford BC3Z-8C471-A, 2011-2016), 6.7L Power Stroke Coolant Crossover Tube (Ford HC3Z-8C471-A, 2017-2019)

replace the water pump at weep-hole failure or bearing growl (primary or secondary circuit pump, per which circuit is affected) ()

water-pump - more than one option: 6.7L Power Stroke Primary (Engine) Water Pump, gen1/gen2, 6.7L Power Stroke Primary (Engine) Water Pump, gen3

Prevalence

common