Product Description
CUMMINS 3900955 OEM EXPANSION PLUG (FREEZE PLUG) – DIPSTICK LOCATION – RAM 5.9L (1989–2002)
The Cummins 3900955 OEM expansion plug (freeze plug) is the small but critical dipstick-side block plug that keeps coolant inside your 5.9L B-series instead of on the ground. If the factory cup plug has rusted, popped out, or gone missing, this genuine Cummins core plug restores a positive seal at the driver-side dipstick location on 1989–2002 Ram 2500/3500 5.9L Cummins. No guessing on size or fitment—this is the exact OE plug engineered for the job.
Unlike generic hardware-store plugs, the 3900955 freeze plug is built to Cummins tolerances for press-fit in the block bore, helping prevent coolant leaks, overheating, and costly engine damage. Pair it with other genuine Cummins expansion plugs from CPP Diesel for a fully sealed block on your 12-valve or 24-valve 5.9L Cummins.
FITMENT
- Engine: 5.9L Cummins B-series (12V & 24V)
- Vehicle: 1989–2002 Dodge/Ram 2500 & 3500 with 5.9L Cummins
- Location: Driver-side block at dipstick tube area (side-of-block freeze/core plug)
- Function: Seals coolant passage at dipstick-side core hole, preventing leaks
- Quantity: Sold individually (check your ESN and block for how many are required)
WHY CHOOSE GENUINE CUMMINS 3900955?
- Direct OE replacement for the factory dipstick-side freeze plug on 5.9L Cummins B-series blocks.
- Correct cup-plug design for proper press fit and long-term sealing.
- Helps prevent coolant loss, overheating, and downtime on work trucks and tow rigs.
- Backed by the reliability and durability you expect from genuine Cummins components.
INSTALLATION NOTES
- Clean the block bore thoroughly and remove any rust, scale, or sealant residue before install.
- Orient the cup plug square to the bore and drive it in evenly using the proper driver or socket.
- Follow the Cummins service manual procedure for your specific ESN regarding sealant use (many are dry installs with a clean bore).
- After installation, pressure test the cooling system and inspect for leaks.
CROSS-REFERENCE / RELATED CUMMINS PARTS
Complete your block sealing job with these related genuine Cummins expansion plugs from CPP Diesel (all links are Cummins-only products):
- CUMMINS 3914035 OEM EXPANSION PLUG (SIDE OF BLOCK) – RAM 5.9L 12V/24V (1989–2002)
- CUMMINS 3922072 OEM FRONT/SIDE EXPANSION PLUG – 5.9L (1989–2002)
- CUMMINS 3920706 OEM EXPANSION PLUG (TURBO DRAIN) – RAM 5.9L/6.7L (1989–2018)
- CUMMINS 3900687 OEM REAR CAM EXPANSION PLUG – 5.9L 12V/24V (1989–2002)
SPECIFICATIONS
Specifications for cummins 3900955
| Brand | Cummins (Genuine OEM) |
| Part Number | 3900955 |
| Product Type | Expansion Plug / Freeze Plug / Core Plug |
| Engine Compatibility | 5.9L Cummins B-series (12V & 24V), various B-series industrial/off-highway applications |
| Primary Vehicle Fitment | 1989–2002 Dodge/Ram 2500 & 3500 with 5.9L Cummins |
| Location on Engine | Driver-side engine block at dipstick tube area (side-of-block core plug) |
| UPC | Not specified by manufacturer (UPC not provided) |
| GTIN | Not specified by manufacturer (GTIN not provided) |
| Shipping Weight | Approx. 0.01 lb (small parcel – counts as a lightweight item in shipments) |
| Shipping Info | Ships from CPP Diesel via standard ground; typically ships same or next business day when in stock. |
| Cross Reference | OE-specific plug for dipstick-side location; use 3900955 for this position. For other block locations, see related Cummins plugs (3914035, 3922072, 3920706, 3900687). |
| E-Codes / Emissions | Not emissions-related (mechanical coolant core plug). |
| Prop 65 | Not listed with a specific Prop 65 warning by the manufacturer. Always handle engine coolant and shop chemicals according to local regulations. |
FAQ
Where does the Cummins 3900955 expansion plug install on my 5.9L?This plug installs in the driver-side block at the dipstick area on 5.9L Cummins engines, sealing the coolant passage at that specific core plug location.
Is this a genuine Cummins freeze plug or an aftermarket copy?
This is a genuine Cummins OEM part, sourced through CPP Diesel. It is not a generic hardware plug or white-box aftermarket substitute.
Do I need to use sealant when installing this plug?
Always follow the Cummins service procedure for your specific ESN. Many applications call for a clean, dry press fit into the bore, while some procedures allow a thin coat of non-hardening sealant. If you are unsure, consult a factory service manual or qualified Cummins technician.
Will this plug fit other Cummins engines besides the 5.9L Ram?
The 3900955 plug is used primarily on B-series 5.9L engines and in some industrial/off-highway applications. For non-Ram or industrial use, verify fitment by engine serial number (ESN) before ordering.
What other expansion plugs should I replace at the same time?
If you are chasing leaks or rebuilding a motor, many customers replace the side-of-block, front/side, rear cam, and turbo drain plugs at the same time using these genuine Cummins parts: 3914035, 3922072, 3920706, and 3900687.
