The Cummins ISX15 (and its marine/industrial counterpart QSX15) is one of the most widely deployed heavy-duty diesel engines in the world — powering freight trucks across North America, mining equipment in Australia and Africa, and marine vessels globally. Its cylinder head is one of the most frequently replaced heavy-duty diesel components, making accurate part number identification and quality sourcing critical for fleet operators and equipment managers.
This guide covers: OEM part numbers and cross-references, common failure modes, diagnosis procedures, repair vs. replace decision, and a complete buying guide for ISX15 / QSX15 cylinder heads. Bookmark this page — it is the most comprehensive ISX15 cylinder head resource available online.
Quick Answer: The Cummins ISX15 cylinder head most commonly fails from head gasket blowthrough (usually caused by overheating or improper installation torque) and thermal fatigue cracks in the combustion chamber floor. EGR cooler deposits can also cause localized overheating and crack propagation. OEM replacement heads are available as complete assemblies with valve seat inserts pre-fitted.
- White exhaust smoke → coolant past head gasket or crack in head
- Engine overheating → head surface warpage prevents head gasket seal
- Low compression on multiple cylinders → head gasket or crack between cylinders
- Oil mixing with coolant → head gasket failure between oil and coolant passages
- Repeated head gasket failures → head surface warpage (needs machining or replacement)
- EGR soot buildup → restricts coolant flow, causes localized overheating
Cummins ISX15 / QSX15 Engine Overview
The Cummins ISX15 is a 14.9-litre (912 cu in) inline-6 heavy-duty diesel engine producing 400–625 hp, used primarily in Freightliner, Kenworth, Peterbilt, and International commercial trucks. The marine/industrial QSX15 shares the same core architecture but is rated for marine propulsion and stationary power generation.
| Specification | ISX15 (Truck) | QSX15 (Marine/Industrial) | Displacement | 14.9L / 912 cu in | 14.9L / 912 cu in | Configuration | Inline-6, 4-valve/cylinder | Inline-6, 4-valve/cylinder | Bore x Stroke | 137 x 169 mm | 137 x 169 mm | Power Output | 400–625 hp @ 1,800–2,000 rpm | 450–600 hp @ 1,800 rpm | Peak Torque | 1,650–2,050 lb-ft | 1,700–2,050 lb-ft | Emissions Standard | EPA 2002 / 2007 / 2010 (EGR+SCR) | EPA Tier 2 / Tier 3 / IMO II | Head Part Numbers | 4962732, 4331187, 4962733 | 4962732, 4331187, 4962733 | Head Gasket | 4025346 / 4025347 | 4025346 / 4025347 | Typical Vehicle | Freightliner Cascadia, Kenworth T680 | Marine vessel, generator set |
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Important: The ISX15 underwent a significant design change in 2013 with the introduction of the CM2350 (EPA 2010 compliant) version. Pre-2013 heads (part numbers 4962732, 4331187) are not interchangeable with post-2013 heads (part number 4962733) without adapter work. Always confirm the engine serial number when ordering.
7 Common Cummins ISX15 / QSX15 Cylinder Head Problems
1. Head Gasket Blowthrough
Head gasket failure is the most common ISX15 cylinder head failure. The ISX15 head gasket is a multi-layer steel (MLS) design that requires precise torque values and a calibrated torque-to-yield (TTY) tightening sequence. Common causes of head gasket failure:
- Running with restricted coolant flow (clogged radiator, failed water pump)
- Using non-OEM head gaskets with incorrect compressibility
- Over-tightening head studs (causes gasket crushing failure)
- Under-tightening head studs (allows gas blowby)
- Coolant contamination from incompatible antifreeze
- Excessive EGR cooler deposits increasing cylinder head temperature
When a head gasket fails on the ISX15, the most common symptom is white exhaust smoke (coolant entering combustion chambers) and a gradual loss of coolant without external leaks. In severe cases, combustion gases enter the coolant system causing the expansion tank to pressurize and overflow.
2. Thermal Fatigue Cracking in Combustion Chamber Floor
The ISX15 runs at high cylinder pressures (up to 2,200 psi peak firing pressure in EPA 2010 engines). Over time, thermal cycling causes micro-cracks to form between valve seats and across the fire ring (combustion chamber sealing surface). These cracks are accelerated by:
- Repeated overheating events (even brief episodes cause cumulative damage)
- Running on low coolant (even for a few minutes)
- EGR cooler failures causing elevated exhaust gas temperatures
- Using non-OEM coolant that lacks proper corrosion inhibitors
- Long idling periods (low coolant flow, high cylinder temperature)
Cracks between adjacent cylinders or across the fire ring require head replacement — welding repair is not reliable in these high-stress areas. A dye penetrant test or ultrasonic crack detection at a machine shop can confirm crack extent.
3. EGR Cooler Deposit Buildup
EGR cooler failures are a known issue on ISX15 EPA 2007 engines. When the EGR cooler leaks exhaust gas into the coolant, or when soot accumulates in the EGR passages on the cylinder head, localized overheating occurs in the cylinder bridge areas (the thin metal between adjacent cylinders). This leads to crack propagation.
EPA 2010 CM2350 engines use an improved EGR cooler design and are less prone to this failure mode. When replacing an ISX15 head on a pre-2010 engine, it is good practice to also replace the EGR cooler and flush the cooling system.
4. Valve Seat and Valve Guide Wear
Valve seats wear on the ISX15 after 600,000–900,000 km, especially in engines that frequently run at high load. Worn valve seats cause:
- Loss of compression → reduced power and fuel efficiency
- Excessive valve clearance noise (tappet rattle)
- Increased oil consumption (oil past worn valve stems)
- Hard starting, especially on cold mornings
Valve seat wear can be addressed by re-cutting the valve seats and installing new valves — this is a machine shop job costing USD 400–800. If the valve seats are cracked (not just worn), the head must be replaced.
5. Cylinder Head Surface Warpage
After any overheating event, the ISX15 cylinder head must be checked for flatness (warpage). Allowable warpage is under 0.05mm (0.002"). Overheating typically causes warpage of the fire ring area first. A warped head cannot be salvaged by re-surfacing if warpage exceeds 0.15mm — replacement is required.
Machine shops can resurface ISX15 heads, but the material removal allowance is limited. Always check with a machinist before committing to a resurfacing job.
6. Injector Cup Wear and Damage
ISX15 engines use integral injector cups (no separate sleeve) in the cylinder head. Over time, the injector cup seating surface can erode from the heat and pressure of the injector tip. This can cause:
- Coolant or oil leaking into the combustion chamber around the injector
- Intermittent misfires when the fuel spray pattern is disrupted
- Carbon buildup on the injector tip from coolant contamination
Injector cup damage is typically visible during a visual inspection of the head. If only the injector cup area is damaged, some machine shops can repair it by installing new injector inserts — but a full head replacement is often more cost-effective.
7. Oil Gallery Corrosion from Coolant Contamination
If a head gasket has been leaking coolant into the oil system for an extended period, the oil passages in the cylinder head become contaminated with coolant. This causes:
- Sludge buildup in oil galleries → restricted oil flow
- Rapid bearing wear from contaminated oil
- Camshaft lobe wear from inadequate lubrication
- Oil pressure warning lights at idle
When coolant contamination is suspected, the entire lubrication system should be flushed and all bearings inspected before reinstalling a new or rebuilt head. Continuing to run with contaminated oil will destroy a new head within weeks.
Cummins ISX15 / QSX15 Cylinder Head OEM Part Numbers
The table below lists verified OEM part numbers for Cummins ISX15 and QSX15 cylinder heads. All numbers are cross-referenced against the Cummins master parts database. Prices are indicative — contact us with your engine serial number for a formal quotation.
| OEM Part Number | Application | Emissions Standard | Notes | 4962732 | ISX15 (pre-2013) | EPA 2002/2007 | Most common part number, widely stocked | 4331187 | ISX15 (pre-2013) | EPA 2002/2007 | Alternate part number, same spec | 4962733 | ISX15 (post-2013) | EPA 2010 / CM2350 | CM2350 specific, not interchangeable with 4962732 | 5346780 | QSX15 (marine) | EPA Tier 3 / IMO II | Marine spec with enhanced corrosion resistance | 4972841 | ISX15 ST (single turbo) | EPA 2007 | Single turbo variant specific | 4972842 | ISX15 (industrial gen-set) | EPA Tier 3 | Industrial/generator set spec | 4025346 | Head Gasket (standard) | All | MLS head gasket, 0.05mm thickness | 4025347 | Head Gasket (thick) | All | MLS head gasket, 0.07mm thickness (for block resurfacing) |
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Head Bolt and Torque Specifications
| Component | Torque Spec | Notes | Head bolts (initial pass) | 130 N·m (96 lb-ft) | Calibrated torque wrench required | Head bolts (final pass — TTY) | 260 N·m + 90° | Torque-to-yield — DO NOT reuse old bolts | Head bolt replacement | Always use new TTY bolts | Reusing stretched bolts causes gasket failure | Valve clearance (intake) | 0.38 mm (0.015") | Check cold, before first start of day | Valve clearance (exhaust) | 0.64 mm (0.025") | Check cold, before first start of day | Injector hold-down torque | 35 N·m (26 lb-ft) | Critical — over/under causes misfire |
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Repair vs. Replace: Decision Guide for ISX15 Cylinder Head
| Situation | Recommended Action | Est. Cost | Lead Time | Head gasket failed, head surface OK | Replace head gasket + resurface head | USD 1,500–3,500 | 7–14 days | Single minor crack < 30mm, not on fire ring | Weld repair at machine shop | USD 800–1,500 | 5–10 days | Multiple cracks or fire ring damage | Full OEM head replacement | USD 3,200–5,500 | 7–21 days | Head surface warpage > 0.15mm | Full OEM head replacement | USD 3,200–5,500 | 7–21 days | EGR cooler damaged (pre-2010) | Replace head + EGR cooler together | USD 4,000–7,000 | 10–21 days | Fleet vehicle, high utilization | Always replace with OEM head | USD 3,200–5,500 | 7–21 days | Engine with > 900,000 km, unknown history | Full head replacement — latent damage risk | USD 3,200–5,500 | 7–21 days |
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Cummins ISX15 Cylinder Head Buying Guide
1. Verify the Correct Part Number
The ISX15 uses at least 3 distinct cylinder head part numbers for different production periods. The most critical distinction is pre-2013 (4962732) vs. post-2013 CM2350 (4962733) — these are not interchangeable. Always provide your engine serial number when requesting a quotation. The serial number is stamped on the left side of the engine block above the oil pan rail.
2. Inspect the Head Before Purchase
Request photos of: (1) the deck face (surface that seals against the head gasket), (2) the valve side, (3) the exhaust manifold face, and (4) the injector bores. Check for: cracks between valve seats, scratches from tooling, signs of previous welding, and injector cup condition. Any crack in the fire ring area disqualifies the head.
3. Ask About Valve Seat Condition
The ISX15 head has hardened valve seat inserts that can wear or crack. If the head has been used in an engine with more than 600,000 km, ask whether the valve seats have been re-cut. New valve seats should be pre-fitted on replacement heads from reputable suppliers.
4. Understand Head Gasket Compatibility
ISX15 head gaskets come in two thicknesses: standard (4025346, 0.05mm) and thick (4025347, 0.07mm). The thick gasket is used when the block surface has been machined (surfaced). When purchasing a head with a machined block, make sure the correct gasket thickness is specified — using the wrong thickness causes head gasket failure within days of installation.
5. Source From a Verified Cummins Distributor
Counterfeit ISX15 cylinder heads have been reported in the aftermarket, particularly from unauthorized suppliers in Southeast Asia. Fake heads often have: casting porosity visible under paint, incorrect valve seat angles, and poor surface flatness. Always verify: (1) OEM part number on the casting, (2) Cummins trademark markings, (3) verifiable provenance. Volgen Power sources all Cummins heads from verified Cummins OEM supply chain partners and provides Certificate of Origin and part number verification with every order.
Featured Cummins ISX15 / QSX15 Parts
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Frequently Asked Questions — Cummins ISX15 Cylinder Head
Q: How do I know if my ISX15 head gasket is blown?
Common signs: white exhaust smoke (coolant burning in combustion chamber), gradual coolant loss without external leaks, milky oil (coolant past head gasket into oil pan), engine overheating, and loss of power under load. A coolant pressure test can confirm head gasket failure without disassembling the engine.
Q: Can I replace just the head gasket on my ISX15 or do I need a new head?
If the head surface is flat (under 0.05mm warpage) and there are no cracks, a head gasket replacement + head resurfacing is sufficient. If the head is cracked or warped beyond 0.15mm, a new OEM head is required. The decision should be made by a machinist who has measured the head surface.
Q: Are ISX15 cylinder heads 4962732 and 4962733 interchangeable?
No. The 4962732 (pre-2013 EPA 2002/2007) and 4962733 (post-2013 EPA 2010 CM2350) are different designs with different bolt patterns and coolant passage configurations. Installing the wrong head will cause head gasket failure. Always verify using the engine serial number.
Q: How long does it take to replace an ISX15 cylinder head?
Labor time: 12–18 hours for a skilled technician with proper tooling. This does not include machining time if the head needs resurfacing (add 2–4 days). Total downtime: 5–21 days depending on parts availability.
Q: What is the weight of a Cummins ISX15 cylinder head?
The ISX15 cylinder head weighs approximately 85 kg (187 lbs) bare. When packaged for international shipping (wooden pallet, export crating), allow 110–120 kg per unit. Sea freight cost is calculated on actual or volumetric weight, whichever is greater.
Q: Do you ship ISX15 cylinder heads internationally?
Yes. Volgen Power ships Cummins ISX15 cylinder heads globally. Sea freight is most cost-effective (20–45 days to major ports). Air freight available for urgent orders (3–7 days). All shipments include commercial invoice, packing list, and Certificate of Origin. We handle all export documentation from China.
Related Articles and Guides
- Cylinder Head OEM Replacement Parts Guide — Complete cross-reference for Cummins, Volvo, Mercedes, and all major brands
- Cylinder Head Repair: When to Fix vs Replace — Full decision matrix and OEM performance restoration guide
- Diesel Cylinder Head Problems: 7 Common Issues — Failure mode overview and diagnosis guide
- Volgen Power Cummins Parts Catalog — Full range of Cummins ISX15, QSX15, and all Cummins engine parts
