Product Description
Cummins 3958645 — Cylinder Head Gasket (Thick, MLS) for 5.9L ISB
MPN: 3958645 | Also Known As: head gasket (thick grade), MLS head gasket | Use Case: For engines with milled head and/or block deck
Why This Part
- ✓ OE multi-layer steel gasket engineered for reliable sealing.
- ✓ Thick grade compensates for resurfaced head/block during rebuilds.
- ✓ Direct-fit for 2003–2007 5.9L ISB (24V common-rail) Ram.
- ✓ Prevents compression/coolant leaks under towing or tune power levels.
Quick Specs
| Type | Multi-Layer Steel (MLS) cylinder head gasket, thick grade |
|---|---|
| OE Part # | 3958645 |
| Application | For use when head and/or block have been resurfaced |
| 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/Off-Highway: Common on QSB5.9 applications; verify by ESN before ordering.
Often Paired With
- Head fasteners: ARP stud kit 247-4202 (popular upgrade) or OE bolts 3927063
- Top-end gasket set (intake/exhaust manifold, valve cover, etc.)
- Fresh coolant & thermostat housing seal (e.g., 3954829)
- Machine shop check: head flatness & surface finish (RA) to OE spec
What’s In The Box
- (1) Genuine Cummins Cylinder Head Gasket — Thick (3958645)
- Fasteners and additional gaskets sold separately (see “Often Paired With”).
Install Tips
- Measure piston protrusion and verify correct gasket grade for your build.
- Follow torque sequence/specs precisely; chase threads and inspect dowels.
- Retorque/inspect after initial heat cycles as required by your fastener choice.
FAQ
WILL THIS FIT MY 2003–2007 5.9L CUMMINS RAM?Yes—this is the OE thick-grade head gasket for 2003–2007 5.9L ISB (24V common-rail) Ram 2500/3500. Always confirm by VIN/ESN.
WHEN SHOULD I USE THE “THICK” HEAD GASKET?Use the thick grade when the cylinder head and/or block deck have been resurfaced during machine work, so compressed thickness restores proper piston-to-head and valve clearances.
CAN I REUSE MY OLD HEAD BOLTS?We recommend new fasteners on any head-gasket job. Many builders upgrade to ARP 247-4202 studs for added clamping, especially with tuning or heavy towing.
IS THIS A GENUINE CUMMINS PART?Yes—OE Cummins MLS head gasket, part number 3958645.
DOES THIS INCLUDE OTHER GASKETS?No—this listing is the head gasket only. Add a top-end gasket set and any needed seals to complete the job.
