3979771 Aftermarket Cummins 5.9L B-Series Aftercooler Complete Assembly | Sawley's Select Marine Parts

🔧 Product Description

Aftermarket replacement Complete Marine Aftercooler Assembly - Replaces Part Number: 3979771

New complete replacement aftercooler assembly for Cummins 5.9L B-series marine diesels. It replaces the 3979771/5267875/5566841 service family used on 6BTA 330/370 Diamond and related QSB 5.9 installations.

⚙️ Key Features

• Complete housing-and-core aftercooler assembly

• Replaces Cummins 3979771, 5267875 and 5566841 service families

• Designed for 6BTA 330/370 Diamond and QSB 5.9 engines

• Copper-nickel seawater core

• Ready for installation after transferring or renewing external fittings and hardware

🧰 Kit / Assembly Contents

• 1 × Complete aftercooler housing assembly - P/N 3979771

• 1 × installed copper-nickel aftercooler bundle/core

• 2 × end-cover positions with integrated water connections

• Mounting hardware, hoses and engine-specific external fittings are not included unless stated

🔄 Supersession & Cross Reference

OEM Supersession Chain:

• 5566841 / 5566843 → Later service references associated with 5267875 and 3979771

• 5267875 → Supersedes/updates 3979771

OEM / Related Numbers:

• 5267875

• 5566841

• 5566843

• 4933308

Aftermarket / Verified Equivalents:

• SMX/Seaboard Marine: AC-BCCOMP complete aftercooler

• Mr Cool: MRC3979771 complete assembly

• Seakamp replacement for Cummins B-series aftercooler

🚤 Compatibility

Commonly used on:

• Cummins 5.9L B-series marine diesel engines

Typically suits:

• Engine / Equipment models:

• 6BTA 5.9 330 Diamond

• 6BTA 5.9 370 Diamond

• QSB 5.9 applications using the same B-series aftercooler architecture

• Output / Engine Rating: Approximately 330HP - 380HP

• Engine / System Type: Inline six-cylinder turbocharged and seawater-aftercooled marine diesel engine

• Year Range: 6BTA Diamond/QSB 5.9 production; serial-dependent

• Serial / Model Identification: Confirm engine serial and whether a complete assembly or bundle-only replacement is required.

🔌 Function

The aftercooler removes heat from turbocharged intake air before it enters the engine. Lower charge-air temperature increases air density, supports clean combustion and controls exhaust temperature under load.

Common signs of failure:

• Loss of power or slow turbocharger response

• Excessive black smoke or elevated exhaust-gas temperature

• Charge-air leakage, hissing or low boost pressure

• Saltwater or coolant entering the intake tract

• Internal corrosion, blocked tubes or failed pressure test

📦 Condition

• New aftermarket replacement part

• Brand new

• Supplied in original or equivalent packaging