Product Description
CUMMINS 3949688 OEM RECTANGULAR RING SEAL – CP3 INJECTION PUMP TO GEAR HOUSING (2003–2018)
The Cummins 3949688 OEM rectangular ring seal is the correct CP3 injection pump–to–gear housing seal used on 2003–2018 Dodge Ram trucks equipped with the 5.9L and 6.7L ISB Cummins engine. This genuine Cummins seal keeps the CP3 gear access cover sealed against fuel and oil leaks, maintaining proper rail pressure and long-term reliability on your common-rail fuel system.
Unlike generic O-rings, 3949688 uses a rectangular cross-section designed specifically for the CP3 gear housing interface. Paired with the factory cover and fasteners, it maintains clamp load through countless heat cycles and high-pressure operation. If you’re pulling the CP3, upgrading the gear, or installing a billet gear cover, this low-cost OEM seal is cheap insurance against future seepage.
- Genuine Cummins 3949688 rectangular ring seal (no knockoffs or re-boxed parts).
- Designed for the CP3 injection pump gear access cover interface.
- Direct fit for 2003–2018 Ram 2500/3500 5.9L & 6.7L ISB applications (see fitment below).
- Commonly used on ISB/QSB industrial engines – always confirm by ESN.
Fitment – Where CUMMINS 3949688 Is Used
Automotive – Dodge Ram Cummins
- 2003–2007 Ram 2500/3500 – 5.9L ISB common-rail Cummins (CP3 pump)
- 2007.5–2018 Ram 2500/3500 – 6.7L ISB common-rail Cummins (CP3 pump)
Position: CP3 high-pressure fuel pump gear access cover / CP3-to-front timing gear housing interface.
Industrial / Off-Highway (Common Examples)
- ISB & QSB 6.7L platforms using a CP3 pump with front timing gear access cover (verify by ESN).
Always confirm by VIN or Engine Serial Number (ESN) when working outside standard Ram 2500/3500 pickup usage.
Related Cummins Components On This Job
- CUMMINS 5273414 OEM CP3 FUEL PUMP DRIVE GEAR – 5.9L (2003–2007) – OEM CP3 drive gear that meshes with this seal’s mounting area.
- CUMMINS 3949326 OEM RING DOWEL – FRONT GEAR HOUSING / CYLINDER BLOCK ALIGNMENT – ISB 5.9L/6.7L (2003–2018) – alignment dowels that keep the timing gear housing correctly located.
- CUMMINS 3906698 OEM WATER PUMP RECTANGULAR RING SEAL – 5.9L/6.7L (1989–2018) – another critical rectangular seal at the water pump-to-block interface.
- CUMMINS 3954829 OEM THERMOSTAT HOUSING SEAL – 5.9L/6.7L (2003–2018) – genuine O-ring for the thermostat housing on the same ISB platforms.
Cross-Reference (For Identification Only)
The Cummins 3949688 rectangular ring seal is commonly crossed to:
- Interstate-McBee: M-3949688 (aftermarket equivalent)
- Reliance: K3949688 (aftermarket equivalent)
- Mopar / Chrysler reference: 5086763AA (Ram application listing)
These part numbers are listed for identification only. CPP Diesel recommends using genuine Cummins 3949688 for best sealing and long-term durability.
What’s In The Box
- (1) Genuine Cummins rectangular ring seal – part number 3949688
Installation Notes
- Clean the CP3 gear housing groove completely – remove all old seal material and debris.
- Lightly lubricate the new seal with clean engine oil or assembly lube before installation.
- Seat the rectangular seal evenly without twisting; ensure it sits fully in the groove.
- Torque the CP3 or cover to OEM specification and recheck for leaks after initial run time.
Specifications for cummins 3949688
| Parameter | Value |
|---|---|
| Brand | Cummins Genuine Parts |
| Part Number | 3949688 |
| Description | Rectangular ring seal – CP3 injection pump to front timing gear housing |
| Engine Platforms | 5.9L ISB (2003–2007), 6.7L ISB (2007.5–2018) Ram 2500/3500; ISB/QSB industrial applications (verify by ESN) |
| Material | Fuel- and oil-resistant elastomer (OEM specification) |
| Shape | Rectangular-cross-section ring |
| UPC | Not specified by Cummins (no public UPC listing found) |
| GTIN | Not specified / not published |
| Shipping Info | Ships as a small, lightweight seal; standard ground or air parcel service. Dimensions approx. 4.00" x 0.17" x 6.25" package. |
| Cross Reference | Interstate-McBee M-3949688; Reliance K3949688; Mopar 5086763AA (identification only, use at your discretion). |
| E-Codes / Emissions | Not emission-calibrated; mechanical sealing component only |
| Prop 65 Warning | This product can expose you to chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, visit www.P65Warnings.ca.gov. |
FAQ – CUMMINS 3949688 RECTANGULAR RING SEAL
WILL THIS SEAL FIT MY 2003–2018 RAM 2500/3500 CUMMINS?
Yes. If your truck is a 2003–2007 5.9L ISB or 2007.5–2018 6.7L ISB with a CP3 pump, this is the OEM rectangular ring seal for the CP3 gear access cover / CP3-to-gear housing interface. Always verify by VIN or ESN when in doubt.
IS THIS THE RECTANGULAR SEAL OR THE ROUND O-RING?
Part number 3949688 is the rectangular-cross-section seal. It is different from the round CP3 cover O-ring used in other locations. If your service info calls out the “rectangular ring,” this is the correct OEM part.
HOW MANY 3949688 SEALS DOES MY ENGINE USE?
Only one 3949688 seal is typically used at the CP3 gear access cover / pump-to-cover interface. Replace it any time the cover or CP3 pump is removed for service.
CAN I USE AN AFTERMARKET CROSS-REFERENCE INSTEAD?
There are aftermarket crosses (Interstate-McBee M-3949688, Reliance K3949688, etc.), but CPP Diesel recommends sticking with genuine Cummins 3949688 for long-term sealing performance—especially on tuned or hard-working trucks.
WHAT OTHER PARTS SHOULD I CONSIDER WHILE I’M IN THERE?
This is the perfect time to inspect and replace related timing gear case hardware and seals: Cummins 5273414 CP3 drive gear, Cummins 3949326 gear housing ring dowel, and cooling seals like Cummins 3906698 water pump rectangular ring and Cummins 3954829 thermostat housing seal.
