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

53-block casting crack (24v ISB)

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

Symptoms

coolant loss with no external leak traces; crusty white/green residue high on the block, under the intake side near the injection pump
in cold climates the crack weeps and can dump coolant fast

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

Root cause

A batch of 24v ISB engine blocks cast at plant #53 (1999-2002) carries thin casting sections behind the injection pump boss that crack under thermal/load cycling. Identified by the raised '53' casting mark on the block. Not repairable in place - the standard outcome is a used non-53 block or a long block.

Diagnosis

locate the '53' casting number on the block side (engraved, ~2 cm) and inspect the pump-boss area for weeping/crusting
pressure-test the cooling system cold and re-inspect the boss area
if buying a used 1999-2002 engine, check the casting number FIRST

Fixes

replace the engine: used non-53 block or a reman long block (the crack itself is not weldable reliably) ()

5.9L Cummins Reman Long Block (2003-2007)

Prevalence

common