Product Description
Genuine Cummins
Cummins 3900955 — Expansion Plug / Freeze Plug (Dipstick Location)
MPN: 3900955 | Also Known As: core plug, cup plug, freeze plug | Location: Driver-side block by dipstick (5.9L)
Why This Part
- ✓ OE block seal for the dipstick-side expansion port—stops coolant leaks.
- ✓ Direct-fit for 1989–2002 5.9L Cummins B-series (12V & 24V).
- ✓ Correct 9.5 mm size for the specified location on B-series blocks.
- ✓ Genuine Cummins quality and corrosion-resistant finish.
OE Fit Stops Leaks 1 Per Location
Quick Specs
| Type | Engine expansion / core plug (freeze plug) |
|---|---|
| OE Part # | 3900955 |
| Size | ~9.5 mm (dipstick-side block location) |
| Qty Required | 1 per dipstick-side location (sold individually) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 1989–1998 | 5.9L Cummins 12-Valve (B-Series) | Dodge Ram 2500/3500 |
| 1998.5–2002 | 5.9L Cummins 24-Valve (B-Series) | Dodge Ram 2500/3500 |
Notes: This plug seals the dipstick-side core hole on 5.9L B-series blocks. Always verify by VIN/ESN.
Often Paired With
- Cooling system service: coolant flush & fresh coolant
- Rust inhibitor / block sealants: as specified by Cummins procedures
- Light sealant: per technician preference for cup plugs (clean, dry bore first)
What’s In The Box
- (1) Genuine Cummins Expansion Plug (3900955)
Install Tips
- Drain coolant; clean the bore to bare metal before installation.
- Lightly coat the plug per shop procedure; drive squarely to seat flush.
- Refill/bleed cooling system; verify no seepage after heat cycle.
FAQ
WILL THIS FIT MY 1989–2002 5.9L CUMMINS RAM?Yes—this is the OE dipstick-location plug for 1989–2002 5.9L Cummins B-series trucks (12V & 24V). Verify by VIN/ESN.
WHERE EXACTLY DOES THIS GO?It installs on the driver’s side of the engine block near the dipstick tube opening (the “dipstick location” freeze plug).
WHAT SIZE IS THE PLUG?Approximately 9.5 mm for this location on the B-series block.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins 3900955 (expansion/core plug) with proper fit and finish.
DOES IT FIT 2003+ 5.9L OR 6.7L ENGINES?This listing targets 1989–2002 5.9L. Later engines use different plug sizes/locations—verify by ESN for 2003+ or 6.7L.
Product Videos
Custom Field
Vehicle Year 1989-2002
Vehicle Make DODGE
ENGINE 5.9L CUMMINS
