Cummins 3959031 — Genuine Engine Oil Cooler Core for ISB 5.9L

MPN: 3959031  |  Also Known As: oil cooler core, stacked-plate oil cooler  |  Cross-Refs: 4896407, 3902434, 3903375

Genuine Cummins oil cooler core engineered to maintain stable oil temperatures and protect bearings, cam, and turbo on ISB platforms. Direct-fit for 2003–2007 5.9L common-rail Ram; gaskets/hardware vary by model year (see notes below). Sold individually (1 per engine).

Features & Benefits

• OE heat rejection to stabilize viscosity and oil pressure under load.
• Direct-fit replacement for ISB 5.9L (03–07) with OEM sealing interfaces.
• Stacked-plate core construction for efficient thermal transfer.
• Reduces risk of bearing & turbo damage from overheated/contaminated oil.
• Backed by Cummins quality for fit, function, and durability.

Verified Fitment (Automotive)

Industrial/Off-Highway: ISB5.9/QSB4.5 circa 2003.5–2007, and used primarily on some Tier 3 ISB/QSB 6.7 applications—verify by ESN before ordering.

Specifications

• Type: Engine oil cooler core (stacked-plate)
• OE Part Number: 3959031
• Cross-References (identification): 4896407, 3902434, 3903375
• Quantity Required: 1 per engine (sold individually)

Often Paired With

• Oil cooler gaskets/seals (year-specific): 4895742, 3864458 (’03–’05) · 3974127, 2830559 (’06–’07/’09)
• Fresh oil & filter: replace after cooler change to flush debris

What’s In The Box

• (1) Genuine Cummins Oil Cooler Core (3959031)
• Gaskets/hardware sold separately (see “Often Paired With”).

Installation Tips

• Inspect/flush lubrication circuit after any internal failure before installing the new cooler.
• Use new gaskets and torque fasteners to factory spec; check for leaks on warm-up.
• Change engine oil & filter after installation and again after initial heat cycle if contamination was present.

FAQ

Will this fit my 2003–2007 5.9L Cummins Ram?

Yes—3959031 is the OE cooler core for 2003–2007 5.9L ISB common-rail Ram 2500/3500 (confirm by VIN/ESN).

Does this come with gaskets?

No—gaskets are sold separately and vary by year. Common choices include 4895742/3864458 for ’03–’05 and 3974127/2830559 for ’06–’07.

What about 2007.5+ 6.7L trucks?

Most 6.7L Ram applications use cooler 3975818. Some industrial Tier 3 ISB/QSB 6.7 engines use 3959031—verify by ESN.

How do I know my cooler is failing?

Low oil pressure, overheating, oil/coolant cross-contamination, or debris after a component failure are common signs. Replace promptly to prevent damage.

Is this a genuine Cummins part?

Yes—OE Cummins part 3959031 for proper fit and durability.