Failure mode - Cummins 5.9L Diesel (Dodge Ram HD)

Head gasket failure on tuned common-rail trucks (03-07)

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

Symptoms

coolant push-out under boost (degas overflow), combustion bubbles in the degas bottle
cleaning up on stock tunes returns - the tell that it is boost, not the cooling system

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

Root cause

The stock head gasket clamps fine at stock boost; elevated boost/EGT on tuned trucks (and missing head-stud preload) lifts the head and the gasket goes. The fix is a gasket set WITH head studs and a proper deck check, not just a re-torque.

Diagnosis

combustion-leak test at the degas neck + boost-event logging (overboost spikes)
inspect for previous 'repair by re-torque' marks on the head bolts

Fixes

head gasket set with ARP head studs (the community-standard upgrade), machined deck check ()

head-gasket-set - more than one option: 5.9L Cummins Head Gasket Set, 12v (PSP MLS, 89-98), 5.9L Cummins Head Gasket Set, 24v (PSP MLS, 98.5-02), 5.9L Cummins Head Gasket Set, common-rail (Mahle / Fire Ring, 03-07)
5.9L Cummins Main Stud Kit (P1, 24v common-rail)

Prevalence

common