Cummins QSB series service intervals

The Cummins QSB (5.9L and 6.7L marine variants) is common in trawlers and midsize motoryachts. Oil and oil filter: every 250 hours or 6 months, use Cummins-approved 15W40 CJ-4 marine diesel oil. Fuel filter (Cummins-branded FS19765 or equivalent Fleetguard): every 250 hours. Water separator: drain daily during operation, replace filter every 500 hours. Air filter: every 500 hours or when the restriction indicator triggers. Coolant: every 2 years or 4000 hours, use Fleetguard ES Compleat OAT (red/orange, not green). Impeller: every 250 hours or annually. Belt inspection: every 250 hours. Zinc anodes on the heat exchanger and aftercooler: inspect every 250 hours, replace at 50 percent consumption. Valve lash: every 1500 hours. Injectors: no scheduled replacement, condition-based. Aftercooler cleaning (raw water side): every 1000 hours in salt water, this is the QSB's Achilles heel, a scaled aftercooler drops power and eventually cracks.