Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, LML 2011-2016; LGH vans 2011-2016)

Cooling system wear: water pump, fan clutch, oil cooler (LML)

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

Symptoms

coolant seepage at the water pump weep hole; bearing growl
overheating under tow traced to a locked/loose fan clutch
oil-cooler service themes carried over from the earlier Duramax era

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 (2 causes)

Root cause

Water pump seals and bearings wear with mileage, fan clutches lock or slip, and oil-cooler lines weep - ordinary wear items that surface under towing loads on high-mileage trucks.

Diagnosis

pressure-test the system; verify thermostat and fan clutch operation under load before radiator replacement
inspect the oil-cooler lines at service intervals

Fixes

replace the failed cooling component; use the correct coolant spec on refill ()

Duramax LML Water Pump (OEM)
fan-clutch - more than one option: Duramax LML Fan Clutch 2011-2014 (OEM), Duramax LML Fan Clutch 2015-2016 (OEM)
Duramax LML Engine Oil Cooler Assembly (OEM)
duramax-lml: thermostat (honest catalog gap)

Prevalence

occasional