Description
Engineered Reliability: Cummins 3900955 Expansion Plug for ISF2.8 Engines
The Cummins 3900955 expansion plug, commonly referred to as a cup plug or freeze plug, is an essential OEM component used to seal core holes in the engine block of Cummins ISF2.8 diesel engines. This high-quality, precision-machined part plays a vital role in maintaining the integrity of the engine cooling system by preventing coolant leaks and resisting corrosion, vibration, and high thermal loads.
Technical Specifications
| Parameter | Details |
|---|---|
| Part Number | 3900955 |
| Component Name | Expansion Plug / Cup Plug |
| Material | High-grade corrosion-resistant carbon steel |
| Application | Cylinder block core hole sealing |
| Compatible Engines | Cummins ISF2.8 diesel engines |
| Installation Type | Press-fit |
| Vehicle Compatibility | Light-duty trucks, commercial vehicles using ISF2.8 |
Function and Application
During engine casting and manufacturing, core holes are used to remove sand and support internal passages. These holes must be effectively sealed before engine operation. The 3900955 plug is press-fitted into these ports to ensure a leakproof seal under high-pressure coolant flow and fluctuating thermal conditions.
In Cummins ISF2.8 engines, which are widely used in light trucks, buses, and construction equipment, this plug ensures the integrity of the engine block by preventing coolant from leaking externally or into unintended internal passages.
Key Features and Benefits
- OEM Precision: Manufactured to Cummins’ exact engineering specifications for perfect dimensional matching and secure installation.
- Long-Lasting Seal: Resistant to rust, chemical corrosion, thermal cycling, and pressure fluctuations.
- Engine Protection: Maintains proper coolant flow within the block, preventing overheating and internal erosion.
- Easy Maintenance Fitment: Ideal for engine rebuilds, servicing, and preventive maintenance routines.
Installation Guidelines
Proper installation is key to achieving a reliable seal:
- Ensure the bore is clean, dry, and free of scale or oil residue.
- Align the plug squarely before driving it evenly into the bore using an appropriately sized installation tool.
- Verify that the plug is seated flush or slightly below the cylinder block surface.
- Perform a coolant system pressure test after installation to confirm integrity.
Common Use Cases
- Replacement during engine overhauls or rebuilds
- Leak repair for worn or corroded expansion plugs
- Preventive maintenance for high-mileage diesel engines
- Essential during cylinder block machining or cleaning
Why Choose the 3900955 OEM Plug?
Genuine Cummins parts like the 3900955 expansion plug provide unmatched quality assurance. Non-OEM alternatives often lack the precise tolerances and metallurgical properties required to withstand the harsh operating environment of a diesel engine. By using authentic components, you extend the service life of your engine and ensure peak performance in every operating condition.
Conclusion
The Cummins 3900955 expansion plug is a small but critical component in the performance and reliability of ISF2.8 diesel engines. Whether you’re rebuilding an engine or performing preventive maintenance, choosing this OEM plug ensures a dependable seal, reduced downtime, and long-term engine health. Trust Cummins engineering for components that meet the demands of real-world applications.
For fleet operators, repair shops, and parts distributors, the 3900955 plug represents a durable and cost-effective solution for maintaining Cummins engine systems at peak performance.
