Product Description
Cummins 3959031 – Genuine Engine Oil Cooler Core for ISB 5.9L (2003–2007)
Protect your 5.9L Cummins investment with the genuine Cummins 3959031 OEM engine oil cooler. This stacked-plate cooler core is engineered by Cummins to restore proper oil temperature control and stabilize oil pressure under heavy load, towing, and high EGT conditions. If your original cooler is clogged, leaking, or contaminated from a prior engine failure, 3959031 is the correct OE replacement for 2003–2007 Ram 2500/3500 trucks with the ISB 5.9L common-rail diesel.
Unlike generic aftermarket coolers, this is an OE Cummins cooler core designed to bolt into the factory housing and interface correctly with Cummins gaskets and the OEM filter head. That means less downtime, fewer leaks, and better long-term bearing, cam, and turbocharger protection.
Key Features
- Genuine Cummins 3959031 stacked-plate engine oil cooler core (not a universal aftermarket copy).
- Direct-fit for 2003–2007 Dodge Ram 2500 & 3500 with ISB 5.9L 24V common-rail.
- Designed to regulate oil temperature and maintain stable oil pressure under towing and heavy-use conditions.
- Helps protect crankshaft bearings, camshaft, lifters, and turbocharger from heat-related wear.
- Engineered to work with Cummins oil cooler gasket set 3977913 and oil filter housing 5289557 for a complete OE lubrication system service.
- Backed by Cummins’ engineering, manufacturing standards, and stringent quality control.
Fitment – ISB 5.9L & Related Applications
- Engine: Cummins ISB 5.9L 24-valve common-rail diesel.
- Truck Fitment (Primary): 2003–2007 Dodge Ram 2500 & 3500 with 5.9L Cummins (all cab and drivetrain configurations; verify by ESN/VIN).
- Other Cummins Platforms (Industrial/Off-Highway): Also used on select Tier 3 ISB/QSB engines and related B-series applications. Always confirm by engine serial number (ESN) before ordering for non-Ram equipment.
Cross-Reference & Related Cummins Parts
The Cummins 3959031 cooler core is commonly cross-referenced under the following identification numbers (ID only – confirm by ESN/application before substituting):
- Cross-Ref IDs (ID only): 4896407 (kit reference), 3902434, 3903375, 141427 and related aftermarket supersessions.
Pair this oil cooler with other genuine Cummins components on CPP Diesel for a complete OE repair:
- Older 5.9L Trucks (1989–2002): CUMMINS 3957544 OEM ENGINE OIL COOLER – 6BT/ISB 5.9L (1989–2002)
- Newer 6.7L Trucks (2007.5–2024): CUMMINS 3975818 OEM ENGINE OIL COOLER – ISB 6.7L (2007.5–2024)
- Oil Filter Housing (Filter Head): CUMMINS 5289557 OEM ENGINE OIL FILTER HOUSING – RAM 5.9L/6.7L (2003–2018)
- Oil Filter Head Adapter: CUMMINS 3909355 OEM ENGINE OIL FILTER HEAD ADAPTER – RAM 5.9L/6.7L (2003–2011)
- Oil Cooler Gasket Set: CUMMINS 3977913 OEM ENGINE OIL COOLER GASKET SET – RAM 5.9L/6.7L (2003–2023)
When Should You Replace the Oil Cooler?
Replace the oil cooler any time you see low hot-idle oil pressure, unexplained overheating, oil/coolant cross-contamination, or metallic debris from a prior engine failure. A restricted or leaking cooler can quickly damage bearings and turbo components. When in doubt, replacing the cooler is cheap insurance compared to a full engine build.
Installation & Service Notes
- Always install with new Cummins gaskets (see gasket set 3977913) – never reuse crushed seals.
- Inspect and clean the oil filter housing and adapter (5289557 and 3909355) before reassembly.
- Torque all fasteners to the Cummins service manual specifications and follow the correct tightening sequence.
- After installation, change engine oil and filter and re-check for leaks after the first heat cycle.
Specifications for cummins 3959031
| Brand | Cummins Genuine Parts |
| Part Number | 3959031 |
| UPC | Not published by Cummins (aftermarket listings show multiple non-OE UPC values) |
| GTIN | Not assigned / not published in Cummins catalog (often listed as “SEM GTIN” in third-party data) |
| Engine Platforms | ISB 5.9L 24V common-rail (primary); select Tier 3 ISB/QSB applications – verify by engine serial number (ESN) |
| Model Years (Ram) | 2003–2007 Dodge Ram 2500 & 3500 with 5.9L ISB Cummins |
| Configuration | Stacked-plate engine oil cooler core; installs in OEM housing; gaskets and hardware sold separately |
| Replaces / Cross-Refs (ID only) | 4896407 (kit reference), 3902434, 3903375, 141427 and related aftermarket supersessions – confirm by ESN |
| E-Codes / Emissions | Used on EPA 2003–2007 light-duty diesel (5.9L Ram) and select Tier 3 ISB/QSB applications; verify per ESN |
| Shipping Weight | Approx. 6.5 lb (cooler core only; packaged weight may vary) |
| Package Dimensions | Approx. 13 in L x 6 in W x 3.5 in H (reference dimensions) |
| Shipping Method | Standard ground shipping; qualifies for free or flat-rate shipping promos where applicable |
| Prop 65 Warning | Yes – This product can expose you to chemicals including lead and other petroleum byproducts, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov. |
FAQ
Will this Cummins 3959031 cooler fit my 2003–2007 5.9L Cummins Ram?Yes. Cummins 3959031 is the correct OE engine oil cooler core for most 2003–2007 Dodge Ram 2500/3500 trucks equipped with the ISB 5.9L common-rail diesel. Because some fleet and export trucks can vary, always confirm by VIN or engine serial number (ESN) if you’re unsure.
What gaskets do I need when replacing this oil cooler?
You should install new Cummins gaskets any time the cooler is removed. For most 2003–2007 5.9L Ram applications, we recommend pairing this cooler with the CUMMINS 3977913 OEM ENGINE OIL COOLER GASKET SET . This kit covers the cooler-to-block and cooler-to-filter head interfaces on 5.9L and 6.7L ISB engines.
Should I replace the oil filter housing or adapter at the same time?
If you see pitting, corrosion, warped surfaces, or debris in the oil filter housing or adapter, it is smart to replace them while servicing the cooler. The most common supporting components are:
- CUMMINS 5289557 OEM OIL FILTER HOUSING – the OE filter head the spin-on filter threads onto.
- CUMMINS 3909355 OIL FILTER HEAD ADAPTER – the adapter between the cooler core and filter housing.
Replacing worn housings and adapters at the same time gives you a clean, leak-free lubrication system.
Is this a genuine Cummins part or an aftermarket replacement?
This is a genuine Cummins OEM engine oil cooler core, part number 3959031. It is not a “will-fit” aftermarket copy. Genuine Cummins components are built to the original engineering specification and validated for durability, flow, and thermal performance.
Do I need to change the engine oil and filter after replacing the cooler?
Yes. Anytime the lubrication circuit is opened, you should change the engine oil and filter. This helps remove residual debris and ensures the new cooler is fed clean oil. If the previous cooler failed catastrophically or there was bearing/turbo damage, you may want to perform multiple short-interval oil changes after the repair.
