CUMMINS 3978517 OEM CYLINDER HEAD GASKET (.020 MARINE) – RAM 5.9L ISB (2003–2007)

Product Description

The CUMMINS 3978517 OEM Cylinder Head Gasket is the genuine multi-layer steel (MLS) head gasket designed to deliver reliable combustion sealing for your RAM 5.9L ISB (2003–2007) or QSB5.9 (CPL 1860/8732) marine/industrial engine. With a +.020″ marine-grade thickness, this gasket compensates for head/block machining or supports high-boost applications — ensuring proper quench, compression, and long-term durability. Built to OEM specifications, it resists blow-by and fluid cross-leaks even under demanding conditions, making it ideal for rebuilds, marine conversions, or high-performance 5.9L ISB builds.

Applications / Fitment: Direct-fit for 2003–2007 RAM 5.9L ISB (24-valve common-rail) and QSB5.9 engines (CPL 1860 & 8732). Always verify engine serial number (ESN) or CPL before ordering to confirm correct thickness and fitment. 

Key Benefits:

• OEM-grade MLS construction for factory-level sealing performance.
• +.020″ marine thickness — ideal for deck/head machining and high-boost applications. 
• Direct replacement for 3978517 — no modifications required.
• Prevents coolant/oil cross-leakage and maintains combustion integrity under heavy load or marine duty.
• Durable fire-ring design ensures long service life and reliable sealing over thousands of hours / miles.

Installation & Maintenance Tips: Always clean oil and coolant passages, verify block and head deck flatness, use new head bolts or studs (re-torque per Cummins spec), and double-check piston protrusion and deck clearance when using .020″ thickness. 

Often Paired With: For a complete head service, pair this gasket with head bolts (e.g. CUMMINS 3927063) or premium head studs, plus upper-gasket sets (intake/exhaust manifold gaskets, valve cover seals), and fresh coolant & oil. 

Cross Reference / Compatible Options:
– For standard-thickness head gasket needs, use the stock-thickness version of part 3978517 (if available).
– Always verify based on ESN / CPL for correct gasket thickness.

WILL THIS FIT MY 2003–2007 5.9L CUMMINS RAM?

Yes — 3978517 is widely used on 2003–2007 5.9L ISB (common-rail) and QSB5.9 platforms. Confirm ESN or CPL and any deck/head machining before purchase. 

IS THIS THE +.020″ MARINE-THICKNESS GASKET?

Yes — this is the +.020″ marine-thickness version. It’s recommended when heads or blocks have been machined, or for high-boost builds. 

HOW DO I PICK THE RIGHT THICKNESS?

Measure piston protrusion and account for deck/head machining. Use +.020″ (this part) to maintain proper quench and compression. If no machining or clearance issues, consider standard-thickness gasket. Always verify against ESN / CPL. 

DO I NEED NEW HEAD BOLTS OR STUDS?

Yes — new OE bolts or quality aftermarket studs are strongly recommended to ensure proper clamping force and long-term sealing reliability. 

IS THIS A GENUINE CUMMINS PART?

Yes — this is the genuine OEM CUMMINS part 3978517, built to factory specs for ISB / QSB 5.9 engines.