Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, LB7-LMM 2001-2010)

Head gasket failures (higher mileage / load)

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

Symptoms

coolant loss without external leaks, combustion gases in the coolant
reported most often on higher-mileage and higher-load engines across all four generations

Compare with the other causes of the same sign on this engine: losing coolant (2 causes)

Root cause

The classic cross-generation Duramax repair in the owner record: stock gaskets age, and elevated cylinder pressures (worn injectors, higher tune, heavy tow) finish them. No authoritative rate statistics.

Diagnosis

block test / chemical test for combustion gases in coolant
rule out EGR-cooler leaks first on LLY+ (they share the degas symptoms)
on teardown: head studs and machined surfaces are part of the repair, not extras

Fixes

head gasket replacement with proper surface prep; studs are the community-standard reinforcement on a re-do ()

Prevalence

occasional

Parts for this repair run about $790-$1,150: see them next to the other repairs on this engine in repair costs.