Product Description
Cummins 3978517 — Cylinder Head Gasket (.020 Marine Thickness)
MPN: 3978517 | Also Known As: head gasket, MLS gasket | Applications: 2003–2007 Ram 5.9L ISB & QSB5.9 (CPL 1860/8732)
Why This Part
- ✓ OE multi-layer steel (MLS) gasket for reliable combustion sealing.
- ✓ +.020" marine thickness helps compensate for deck/head machining and supports high-boost builds.
- ✓ Direct-fit for 2003–2007 Ram 5.9L ISB; widely used on QSB5.9 marine/industrial.
- ✓ Durable fire-ring design resists blow-by and fluid cross-leaks.
Quick Specs
| Type | Cylinder Head Gasket (MLS) |
|---|---|
| OE Part # | 3978517 |
| Thickness | +.020" marine |
| Qty Required | 1 per engine (sold individually) |
Verified Fitment (Automotive)
| Year Range | Engine | Chassis |
|---|---|---|
| 2003–2007 | Ram 5.9L ISB (24V Common-Rail) | Ram 2500/3500 |
Industrial/Marine: QSB5.9 (incl. CPL 1860 & 8732). Always confirm by ESN/CPL to ensure the correct thickness.
Often Paired With
- Head Bolts: Cummins 3927063 (set of 26) or ARP 247-4202 head studs
- Upper gasket items: intake/exhaust manifold gaskets, valve cover seals
- Fresh coolant & oil after head service
What’s In The Box
- (1) Genuine Cummins Cylinder Head Gasket (.020) — 3978517
- Fasteners & additional gaskets sold separately (see “Often Paired With”).
Install Tips
- Verify gasket thickness based on piston protrusion and any machining.
- Check deck/head flatness and surface finish; clean oil & coolant passages.
- Use new bolts/studs and torque in proper sequence and stages per Cummins spec.
FAQ
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 thickness by ESN/CPL and piston protrusion.
IS THIS THE +.020" MARINE-THICKNESS GASKET?Yes—this listing is the +.020" marine thickness version, favored when the head/block has been machined or for high-boost builds.
HOW DO I PICK THE RIGHT THICKNESS?Measure piston protrusion and account for any deck/head machining. Choose thickness to maintain proper quench and compression.
DO I NEED NEW HEAD BOLTS OR STUDS?Yes—new OE bolts (3927063) or ARP studs are recommended for consistent clamping and long-term sealing.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins 3978517 with MLS construction and factory-specified sealing layers.
