Brand New Cummins ISX15 / X15 Single Overhead Cam Fully Loaded Cylinder Head — 4374091

Engineered for reliability | Backed by 1-year warranty

This is a brand new cylinder head — not remanufactured, not refurbished — for Cummins ISX15 and X15 single overhead cam engines. Precision machined to meet or exceed OEM standards and fully loaded, it is the direct replacement for a cracked or worn factory head without the gamble of a reman core that already failed once.

Key Features

• Brand new casting — zero hours, not remanufactured or refurbished

• Fully loaded — valve train components installed and ready to bolt on

• Precision machined for exact fit and performance

• High-strength materials built for heavy-duty cycles

• 1-year warranty — no core charge, no core return

Choose Your Stage

• Stage 2 (Reinforced) — upgraded casting, standard valve package

• Stage 3 Loaded — Inconel intake & exhaust valves for high-heat, high-load duty

• Stage 4 (Fire Rings) — for fire-ringed applications; made to order, estimated prep time 1–3 days

Fitment

Cummins ISX15 and X15 single overhead cam (SOHC) engines. Not for early dual-overhead-cam ISX applications — if you are unsure which you have, send us your engine serial number and we will confirm before you order.

Complete the Job

ISX head bolts are torque-to-yield and single-use — every head swap needs the ISX / X15 Head Bolt Kit (3678506 / 3678804), one kit for every year 1999–2026, standard or cryo treated.

Doing the head only? Add the ISX15 Head Gasket Set (4376104) or X15 Upper Gasket Set (5406187).
Doing a full in-frame overhaul? Skip the gasket set — your overhaul kit already includes it.

OEM Cross Reference Numbers

3686432 | 3686434 | 3686660 | 3686774 | 3686880 | 3686881 | 3687607 | 3688761 | 3688800 | 4298235 | 4298236 | 4298237 | 4298238 | 4356434 | 4386009 | 5394197 | 5394198 | 79438920 | 79457900 | 79469386 | 79527893 | 79575425 | 4374091

Note: please confirm compatibility with your engine serial number prior to purchase. Contact us if you need assistance.

PLEASE NOTE: FIRE RING HEADS ARE MADE TO ORDER, ESTIMATED PREP TIME IS 1-3 DAYS.

Frequently Asked Questions

Is this a new head or a remanufactured head?
New. A remanufactured head starts as a used core that has already been through hundreds of thousands of heat cycles. This casting has zero hours on it.

Will this fit my ISX?
It fits ISX15 and X15 single overhead cam engines. Early ISX engines with dual overhead cams use a different head — send us your ESN and we will verify.

How do I know if my ISX head is cracked?
Coolant loss with no external leak, white smoke on cold start, combustion gases in the coolant, and overheating that a thermostat does not fix. A pressure test confirms it.

Do I need to return my old head?
No — no core charge, no core return required.