Cummins — Aftercooler Housing O-Ring ISB QSB — 3919853
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The Cummins 3919853 O-Ring Seal is a factory Cummins sealing gasket used on select Cummins diesel engine assemblies, including marine aftercooler and turbocharger-related sealing locations where the parts diagram calls for this number. In marine service, 3919853 is commonly known as the thin aftercooler core housing O-ring. It is used to seal the aftercooler core housing interface and help prevent coolant seepage, boost-air leakage, and loss of proper charge-air cooling performance.
Key Features
- Cummins part number: 3919853
- Product type: O-ring seal / sealing gasket
- Common marine reference: Thin aftercooler core housing O-ring
- Primary service location: Aftercooler core housing sealing area on applicable Cummins engines
- Additional application context: Used in select Cummins turbocharger or air-system sealing locations where specified by parts diagram
- Fitment identifier: Used on housings with the narrow casting gap, approximately 0.070" between the bolt hole and casting edge
- Related service kit reference: 4025341
- Related alternate-size O-ring: 4019975 “fat” aftercooler O-ring for wider-gap housings
Engine Compatibility
This O-ring is commonly associated with select Cummins medium-duty, industrial, and marine diesel platforms, including applications in the following engine families:
- Cummins 5.9L ISB / QSB
- Cummins 6B5.9
- Cummins 6C8.3
- Cummins QSB6.7
- Tier 3 5.9L ISB / QSB marine applications where the aftercooler housing calls for the thin 3919853 seal
Fitment must be confirmed by engine serial number, CPL, aftercooler housing design, and Cummins parts diagram.
Serial Number Fitment Notice
Cummins used more than one aftercooler core housing O-ring profile depending on casting design. The 3919853 is the thin version and is typically used when the aftercooler housing has a narrow approximately 0.070" gap between the bolt hole and the edge of the casting. Engines with the wider casting gap may require the 4019975 fat O-ring instead.
Before ordering, confirm the engine serial number, CPL, aftercooler housing casting, and original O-ring profile. Do not select this seal by engine displacement alone.
When This Part Needs Replacement
Replace this O-ring whenever the aftercooler core is removed, the aftercooler housing is opened, or the seal shows flattening, cracking, swelling, hardening, cuts, or compression set. It should also be inspected if there are signs of coolant seepage, boost-air leakage, corrosion staining, salt deposits, reduced charge-air cooling performance, or unexplained performance loss.
A used aftercooler O-ring should not be reused after disassembly, especially on marine engines exposed to heat cycling, vibration, coolant, boost pressure, and salt-air operating conditions.
Installation Notes
Clean the aftercooler housing groove and mating surfaces before installing the new O-ring. Inspect the aftercooler core, housing casting, bolt holes, sealing lands, and corrosion-prone edges before reassembly. Make sure the O-ring sits evenly in the groove and is not twisted, stretched, pinched, or cut during installation.
Follow the Cummins service procedure for aftercooler removal, cleaning, pressure testing, reassembly, and torque sequence. If the aftercooler has been removed for cleaning or service, inspect related seals, gaskets, hoses, clamps, and mounting hardware before returning the engine to service.
Alternate/Superseded Part Numbers
- Cummins: 3919853
- Related Cummins service kit reference: 4025341
- Related larger-profile aftercooler O-ring: 4019975
- Common description: Thin aftercooler core housing O-ring
Parts Desk Insight
The critical detail on this Cummins aftercooler seal is the housing profile. The 3919853 thin O-ring and the 4019975 fat O-ring are not interchangeable just because the engine family looks similar. Match the seal to the aftercooler casting gap, engine serial number, and Cummins parts diagram before ordering.
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Returns & warranty
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