Failure mode - Cummins 6.7L ISB (Ram HD)

EGR cooler failure

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

Symptoms

white sweet-smelling smoke, coolant loss with no external leak
EGR cooler DTCs / flow codes; coolant smell at the exhaust
pressurised cooling system (bubbles at the degas bottle)
in bad cases: hydro-lock symptoms / white smoke clouds at startup

Root cause

The EGR cooler passes hot exhaust through coolant; thermal cycling and soot loading crack it. Bostech notes 2007.5-2009 and 2010+ coolers are DIFFERENT hardware (different service PNs) - order by year. Coolant condition and overheat events accelerate cracking; unlike the 6.0 Power Stroke the oil cooler is not the usual precursor here.

Diagnosis

block-test the coolant for combustion gas (careful: EGR cooler gas also shows)
compare EGR cooler temp vs coolant temp PIDs at startup (should track until warm-up completes)
pressurise the cooling system and watch for immediate pressure rise through the EGR side
pull the EGR valve and look for wet/coolant traces in the passage

Fixes

replace the EGR cooler with the correct-era unit (2007.5-2009 vs 2010+ are different hardware); flush and refill with spec coolant ()

egr-cooler (part category - specific model not chosen)
coolant (part category - specific model not chosen)

Prevalence

common