Failure mode - Cummins 6.7L ISB (Ram HD)

Fuel dilution of engine oil (failed regens)

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

Symptoms

oil level RISING between services (fuel accumulating)
fuel smell on the dipstick; sheen
diluted oil risk: bearing wear, reduced film strength; DPF-era trucks on city cycles worst

Root cause

Late in-cycle fuel injection for DPF regens wets cylinder walls; aborted regens (short trips) leave the fuel in the oil. Worst on 2007.5-2012 DPF-only trucks with city duty cycles; improved (fewer, hotter regens) on 2013+ SCR trucks. Compounded by injector seal blow-by (see the injector mode).

Diagnosis

track oil level between changes - a rising level on a diesel is fuel or coolant, never good
sniff/sheen the dipstick; lab oil analysis (fuel %) for confirmation
review regen frequency/aborts in the ECM; cross-check injector health

Fixes

shorten oil-change intervals on city-cycle trucks; verify regens actually complete (duty cycle) ()

engine-oil (part category - specific model not chosen)

address contributors: injector seals, stuck VGT preventing regen completion ()

injector-seal-kit (part category - specific model not chosen)
vgt-turbo (part category - specific model not chosen)

Prevalence

occasional