Komatsuengine(no series)
Komatsu S6D125-1E(S/N 10001-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu S6D125-1E (S/N 10001-UP) is a 6-cylinder, turbocharged, aftercooled diesel engine belonging to the Komatsu 125 series. It delivers approximately 275 hp (205 kW) and 1,010 lb-ft (1,370 Nm) of torque. This powerplant was installed in mid-size to heavy construction equipment, including the PC400 series excavators, D65 series crawler dozers, and WA470 series wheel loaders. Production years span the late 1990s through the 2000s. It succeeded earlier 6D105 and 6D110 series engines and was eventually replaced by the S6D125-2 and SAA6D125-2 series as emissions regulations tightened. Configurations varied by application, with wet cylinder liners and mechanical fuel injection being standard for this generation.
The S6D125-1E remains critical in the used and parts market due to its widespread installation in the PC400 and D65 platforms, which are still active in secondary markets. The transition to the S6D125-2 series introduced electronic control and different emissions packages, making the S6D125-1E a preferred choice for operators seeking simpler, mechanical reliability. Its robust cast-iron block and wet liner design allow for extensive rebuildability. The engine's compatibility across excavators, dozers, and loaders creates a large, liquid aftermarket for cores, overhaul kits, and individual components, sustaining its value long after original equipment production ceased.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Komatsu S6D125-1E(S/N 10001-UP) specifications
Engine
| Model | S6D125-1E (S/N 10001-UP) |
| Type | 4-cycle, water-cooled, inline vertical, direct injection, turbocharged and aftercooled |
| Displacement | 11 L |
| Cylinders | 6 |
| Gross Power | 202 kW (275 hp) |
| Net Power | 205 kW (275 hp) |
| Torque | 1,370 N·m (1,010 lb·ft) |
| Emissions Tier | Not documented for this exact serial range — verify with your dealer |
Weights
| Operating Weight | Not documented for this exact serial range — verify with your dealer |
| Shipping Weight | Not documented for this exact serial range — verify with your dealer |
| Ground Pressure | Not documented for this exact serial range — verify with your dealer |
Dimensions
| Transport Length | Not documented for this exact serial range — verify with your dealer |
| Transport Width | Not documented for this exact serial range — verify with your dealer |
| Transport Height | Not documented for this exact serial range — verify with your dealer |
| Track Gauge | 1,880 mm (74.0 in) / 2,050 mm (80.7 in) |
| Ground Clearance | 400 mm (15.7 in) / 510 mm (20.1 in) |
Performance
| Travel Speed | Not documented for this exact serial range — verify with your dealer |
| Gradeability | Not documented for this exact serial range — verify with your dealer |
Service capacities (summary)
| Fuel Tank | Not documented for this exact serial range — verify with your dealer |
| Hydraulic System | Not documented for this exact serial range — verify with your dealer |
| Engine Oil | Not documented for this exact serial range — verify with your dealer |
| Cooling System | Not documented for this exact serial range — verify with your dealer |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
S6D125-1E(S/N 10001-UP) fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (with filter) | Not documented for this exact serial range — verify with your dealer | Komatsu Genuine Diesel Engine Oil, SAE 15W-40 for normal ambient temperatures; SAE 10W-30 for colder climates. Equivalent: Chevron Delo 400 series diesel engine oil built to the same Komatsu engine-oil specification. |
| Cooling system | Not reliably documented for this exact serial range. Closely related earlier D-series generations of similar displacement ran roughly 42-63 L (11.1-16.6 gal), but this figure is not confirmed as applicable to the 6D125-1A S/N 10001-UP - verify with dealer | Komatsu Super Coolant, supplied as concentrate mixed 50/50 with water (extended-life, all-season, anti-corrosion coolant). No separate winter/summer concentration split is called out beyond the standard 50/50 mix; use a higher concentrate ratio only for extreme cold per Komatsu's coolant freeze-protection chart. |
| Fuel tank | 250-320 L (66-85 gal), varies by dozer model; not a fixed engine-level figure | Automotive diesel fuel (ASTM D975 No. 2-D equivalent) for normal conditions; switch to a lighter No. 1-D-equivalent fuel in cold weather per Komatsu's ambient-temperature fuel guidance. Keep tank topped up at end of shift to reduce condensation. |
| Transmission/powertrain compartments | Not separately published for this serial range. The D50A/P-17 uses a manually shifted spur-gear transmission (5 speeds forward, 4 reverse) with splash-type lubrication, sharing lubrication with the spiral bevel gear shaft and the wet multiple-disc steering clutch/band brake, per the factory specifications section; no standalone capacity figure was accessible. | Komatsu Powertrain & Micro Clutch Oil (drive-train fluid spec): SAE 10W in cold conditions, SAE 30 in normal/warm conditions. Equivalent cross-reference: Chevron Delo TorqForce in matching viscosity grade. |
| Final drives (each) | Not separately published for this serial range. Final drive is a 2-stage spur-gear reduction with splash-type lubrication per the factory specifications section; Komatsu shop literature for this chassis does not show it as an independently drained/filled compartment separate from the power train case in the data reviewed. | Komatsu Powertrain & Micro Clutch Oil, same grade as the power train case (SAE 10W cold / SAE 30 normal), unless the periodic maintenance chart calls out a dedicated final-drive fill point with Komatsu Gear Lubricant (SAE 80W-90 or 85W-140, API GL-5 class) - confirm which applies before servicing. |
| Hydraulic system and tank | No standalone hydraulic tank capacity is published; the hydraulic tank is integrated into the control valve assembly, so there is no separate reservoir on this chassis. | Komatsu hydraulic oil (46AW hydraulic fluid spec), ISO VG 46. Equivalent cross-reference: Chevron Rando HD or Delo TorqForce hydraulic-oil equivalents in ISO 46 grade. A Komatsu biodegradable hydraulic fluid option also exists under the same specification for environmentally sensitive sites. |
| Grease (spec only) | Not applicable (grease points serviced per periodic lubrication schedule, not a fill volume) | Komatsu Lithium-base Grease EP2 (G2-LI), NLGI 2, general-purpose chassis grease for normal temperatures. Equivalent cross-reference: Chevron/Delo Grease ESI EP, NLGI 2. Use a lower-consistency (arctic-grade) NLGI 1 or 0.5 lithium grease in sustained sub-freezing climates per standard Komatsu cold-weather guidance. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Komatsu S6D125-1E(S/N 10001-UP) maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
Servicing the S6D125-1E(S/N 10001-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
Monitor KOWA oil analysis results at every 500-hour interval to track wear metals like iron and copper, indicating piston ring or bearing wear. Check coolant SCA concentration regularly; depletion leads to wet liner cavitation pitting. Inspect the air filter restriction indicator daily in dusty conditions. Log engine oil pressure and coolant temperature trends at each start to detect gradual drift before failure. Verify DEF levels on Tier 4 variants to prevent ECM derating. Use Komatsu Super Coolant AF-NAC to maintain proper pH and glycol content, preventing corrosion in the aluminum and cast iron cooling passages.
Corrective & Common Repairs
Address coolant leaks into the crankcase promptly, often caused by failed wet cylinder liner O-rings or cracked liners from cavitation. Replace worn steering clutch and brake linings in dozers to maintain track control. Inspect the hydraulic control valve assembly for leaks, as it serves as the hydraulic tank. Check the turbocharger shaft play and seal condition. Replace the fuel injection pump seals if fuel dilution is detected in the oil. Inspect the oil cooler element for internal cross-contamination between engine oil and coolant. Verify the condition of the vibration damper and crankshaft pulley bolts.
Overhaul & Rebuild Points
Plan an inframe overhaul when compression drops below specification or blow-by exceeds limits, typically around 10,000 to 15,000 hours depending on maintenance history. Replace piston rings, piston pins, and rod bushings. Inspect cylinder liners for scoring or out-of-round conditions; hone or replace as needed. Check main and rod bearing clearances. Replace the turbocharger if shaft end-play is excessive or blades are damaged. Inspect the cylinder head for warpage and replace valve seats if necessary. Ensure the crankshaft is within tolerance for grinding or replacement.
Seasonal & Environment Servicing
In cold climates, verify coolant concentration to prevent freezing and check battery capacity, as the mechanical engine lacks electronic cold-start assist beyond glow plugs. Use lower viscosity engine oil (e.g., SAE 10W) for cold starts. In hot, dusty environments, shorten air cleaner service intervals and keep the radiator and oil cooler fins clear of debris. Inspect the fan belt tension regularly, as heat accelerates wear. Check the thermostat housing for leaks. Ensure the cooling system is flushed and refilled with fresh Super Coolant to prevent scaling and corrosion in high-temperature operation.
S6D125-1E(S/N 10001-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| ND092220-0040 | Filter,Fuel | Fuel system service | Check fitment → |
| 6125-81-7032 | Element Ass'Y,Air Cleaner | Air intake service | Check fitment → |
| 600-181-4300 | Element Ass'Y,Outer | Scheduled service item | Check fitment → |
| ND090438-0420 | Shim? 1.9mm,Element Holder | Scheduled service item | Check fitment → |
| ND090438-0490 | Shim? 2.25mm,Element Holder | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
S6D125-1E(S/N 10001-UP) fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CA115 | Engine crankshaft speed sensor and backup speed sensor failure | Faulty speed sensor, broken wiring harness, or corroded connector at the pin connector | Replace the speed sensor and verify voltage at the pin connector |
| CA111 | Internal engine controller fault | Electronic Control Module (ECM) internal failure | Replace or reprogram the ECM |
| CA451 | Common rail pressure sensor feedback value too high | Malfunctioning rail pressure sensor or actual overpressure condition | Diagnose the fuel rail pressure sensor or check pump lines |
| CA452 | Common rail pressure sensor feedback value too low | Fuel rail pressure sensor error or low pressure condition | Diagnose the fuel rail pressure sensor or check pump lines |
| CA122 | Intake air pressure sensor feedback voltage too high | Intake pressure sensor malfunction or wiring issue | Verify the intake pressure sensor and wiring |
| CA123 | Intake air pressure sensor feedback voltage too low | Sensor short or airflow restriction | Check for a sensor short or an airflow restriction |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration, engine load cycle, or operator misuse |
| CA441 | Battery voltage too low | Weak battery or alternator failure | Replace the alternator or battery; check the voltage regulator |
| CA442 | Battery voltage too high | Alternator overcharging or voltage regulator failure | Replace the alternator or battery; check the voltage regulator |
| CA153 | Intake air temperature sensor feedback voltage too high | Intake air temperature (IAT) sensor error | Replace or test the IAT sensor |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
S6D125-1E(S/N 10001-UP) attachments & work tools
Crawler Dozer Blades & Rippers
The S6D125-1 engine powers the D65E-12, D65P-12, D65EX-12, and D65PX-12 dozer series. These machines utilize standard dozer blades and ripper attachments compatible with the D65 size class. Factory configurations include ROPS cabs or canopies, which affect overall machine height and weight specifications.
Crawler Excavator Buckets & Tools
The engine is fitted to the PC300-3, PC400-3, PC400-5, and PC400LC-5 excavator families. Typical work tools include digging buckets with capacities around 4.5 m³ for the PC400 class. Hydraulic arrangements require specific kit configurations to match the pump output of the S6D125-1 powertrain.
Wheel Loader Buckets & Attachments
Applications include the WA380-1, WA380-3, WA470-3, and WA1200-3 wheel loaders. Work tools consist of standard loader buckets sized for the respective machine class. Hydraulic system compatibility is verified against the engine's turbocharged and aftercooled configuration.
Fluids & Maintenance Specifications
Komatsu specifies genuine lubricants including Diesel Engine Oil (EO/TO series), Hydraulic Oil (HO series), and Super Coolant AF-NAC. The S6D125-1 engine uses wet cylinder liners requiring supplemental coolant additive to prevent cavitation pitting. Oil and coolant capacities vary by specific machine model (e.g., PC400LC-5 vs. WA470-3) and must be referenced in the respective operation and maintenance manual.
All S6D125-1E(S/N 10001-UP) assemblies by section
Every catalogued assembly group for the Komatsu S6D125-1E(S/N 10001-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Cooling System
Komatsu : S6d125-1e(S/N 10001-Up) : Cooling System : Cooling Fan And Mounting
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 22 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***95 | Bolt,(For 2nd Travel Speed) (Op) | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cooling System : Corrosion Resistor And Piping
Komatsu : S6d125-1e(S/N 10001-Up) : Cooling System : Water Pump And Mounting
| 01***30 | Bolt,(For France Noise Suppression) | 2 |
| 01***16 | Bolt (With Air Heater & Conditioner) | 6 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Cylinder Block
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Camshaft
| 01***22 | Bolt | 2 |
| 04***25 | Key, Plain Woodruff | 1 |
| 04***12 | Ring,Snap (For Ripper) | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Crankshaft
| 01***25 | Bolt,(Without Rops Guard? Canopy) | 6 |
| 01***30 | Bolt | 1 |
| 01***35 | Screw | 5 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Crankshaft (Noise Suppression Spec. For Ec)(#33163-)
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Cylinder Block
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 14 |
| 04***14 | Pin, Dowel | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Cylinder Block Cover
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing
| 01***45 | Bolt,(For Suction? Reversible Fan) | 2 |
| 01***45 | Bolt,(For Slag Handling) | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing (Noise Suppression Spec. For Ec)(#33163-)
| 01***45 | Bolt,(For Suction? Reversible Fan) | 2 |
| 01***45 | Bolt,(For Slag Handling) | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Front Cover And Front Support
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***60 | Screw | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Front Cover And Front Support (Noise Suppression Spec. For Ec.)(#33163-)
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***60 | Screw | 1 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 8 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Oil Pan
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 31 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 7 |
| 01***16 | Washer,Radio Controlled Slag Handling | 38 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Oil Pan (Anti-Corrosive Type) (For Slag Handling)(#27258-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 31 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 7 |
| 01***16 | Washer,Radio Controlled Slag Handling | 3 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Block : Piston And Connecting Rod
| 02***13 | Pin, Dowel | 2 |
| 04***18 | Ring, Snap | 2 |
| 61***31 | Piston Ring Ass'Y | 6 |
Cylinder Head
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Air Cleaner And Mounting
| 01***40 | Bolt,(Dust And Dirt Protection) | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 8 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Air Intake Manifold And Connection
| 01***10 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 13 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Cylinder Head(#10001-26750)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 8 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Cylinder Head(#26751-)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 8 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Exhaust Manifold And Turbocharger
| 01***80 | Bolt, Mount Strainer Flange | 2 |
| 01***00 | Bolt (M10-1.50x100) | 16 |
| 01***45 | Screw | 4 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Muffler And Mounting
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***55 | Bolt,(For Suction? Reversible Fan) | 4 |
| 01***30 | Bolt,Radio Controlled Slag Handling | 4 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Rocker Arm And Housing
| 01***95 | Bolt,(For 2nd Travel Speed) (Op) | 2 |
| 01***08 | Nut,R.H. Thread | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 42 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Rocker Arm Housing Cover
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***25 | Bolt, Mount Filter To Bracket | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Turbocharger(#10001-23192)
| 61***00 | Turbocharger Ass'Y,(Tv7705) | 1 |
| GA***85 | V-Band Ass'Y | 1 |
| GA***07 | Rotor Ass'Y | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Turbocharger(#23193-)
| 61***10 | Turbocharger Ass'Y,(Ta4532) | 1 |
| GA***60 | V-Band | 1 |
| GA***52 | Center Housing A | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Water Manifold And Thermostat(#10001-13376)
| 02***43 | O-Ring,Water Manifold | 10 |
| 07***15 | Plug,(Used When Without Heater) | 2 |
| 08***00 | Sensor,Water Temp. And T/C Oil Temp | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Cylinder Head : Water Manifold And Thermostat(#13377-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***15 | Plug,(Used When Without Heater) | 2 |
| 08***00 | Sensor,Water Temp. And T/C Oil Temp | 1 |
Electrical System
Komatsu : S6d125-1e(S/N 10001-Up) : Electrical System : Alternator (13a)
| 60***50 | Alternator A. (13a),(With Non Hardening Pulley) | 1 |
| KD***31 | Bushing,Insulator | 2 |
| KD***72 | Slip Ring Ass'Y | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Electrical System : Alternator And Mounting (13a)
| 01***80 | Bolt,(Not Shown) | 1 |
| 01***30 | Bolt | 1 |
| 01***11 | Nut (Welded) | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Electrical System : Starting Motor (7.5kw)(#10001-19030)
| 60***30 | Starting Motor Ass'Y,(7.5kw)(See Fig.0661) | 1 |
| KD***20 | Magnetic Switch Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Komatsu : S6d125-1e(S/N 10001-Up) : Electrical System : Starting Motor (7.5kw)(#19031-)
| 60***22 | Starting Motor A.,(7.5kw)(See Fig.0661a) | 1 |
| SD***X0 | Bearing,Ball | 1 |
| SD***X0 | Armature Ass'Y | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Electrical System : Starting Motor And Mounting (7.5kw)
| 01***40 | Bolt,(With Center Guard) | 3 |
| 60***30 | Starting Motor Ass'Y,(7.5kw)(See Fig.0661) | 1 |
| 60***22 | Starting Motor A.,(7.5kw)(See Fig.0661a) | 1 |
Fuel System
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Filter And Piping
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#10001-12014)
| DK***00 | Nut | 2 |
| DK***00 | Bolt | 4 |
| DK***00 | Bolt | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#12015-23192)
| DK***00 | Coupling,Cross | 1 |
| DK***60 | Coupling Ass'Y | 1 |
| DK***00 | Nut | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#23193-36093)
| ND***50 | Bolt | 1 |
| ND***40 | Bolt | 2 |
| ND***61 | Bolt | 6 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#36094-)
| ND***50 | Bolt | 1 |
| ND***40 | Bolt | 2 |
| ND***61 | Bolt | 6 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#10001-12014)
| DK***20 | Bolt, Joint | 1 |
| DK***00 | Valve,Check | 2 |
| DK***90 | Feed Pump Ass'Y | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#12015-23192)
| DK***20 | Bolt, Joint | 1 |
| DK***00 | Valve,Check | 2 |
| DK***90 | Feed Pump Ass'Y | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#23193-36093)
| ND***40 | Washer? 1mm,Plate | 1 |
| ND***00 | Pump Ass'Y,Priming Pump | 1 |
| ND***70 | Washer,Union | 4 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#36094-)
| ND***40 | Washer? 1mm,Plate | 1 |
| ND***70 | Washer,Union | 4 |
| ND***10 | Spring, Check Valve | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#10001-12014)
| DK***20 | Flyweight Ass'Y | 1 |
| DK***20 | Guide Lever Ass'Y | 1 |
| DK***00 | Nut,Lock | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#12015-23192)
| DK***20 | Flyweight Ass'Y | 1 |
| DK***20 | Guide Lever Ass'Y | 1 |
| DK***00 | Nut,Lock | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#23193-36093)
| ND***40 | Plate,Thrust | 1 |
| ND***40 | Plug,Screw | 1 |
| ND***10 | Adapter | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#36094-)
| ND***40 | Plate,Thrust | 1 |
| ND***40 | Plug,Screw | 1 |
| ND***10 | Adapter | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#10001-12014)
| DK***00 | Nut,Cap | 1 |
| DK***00 | Cover | 1 |
| DK***40 | Bolt | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#12015-23192)
| DK***00 | Nut,Cap | 1 |
| DK***00 | Cover | 1 |
| DK***40 | Bolt | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#23193-36093)
| ND***70 | Arm,Spring | 1 |
| ND***20 | Washer? 1.0mm,Cover Plate | 2 |
| ND***40 | O-Ring | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#36094-)
| ND***70 | Arm,Spring | 1 |
| ND***20 | Washer? 1.0mm,Cover Plate | 2 |
| ND***90 | Seal,Oil | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#10001-12014)
| 61***31 | Injection Pump A.,(See Fig.0451) | 1 |
| DK***30 | Bearing,Roller | 2 |
| DK***00 | Camshaft | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#12015-23192)
| 61***32 | Injection Pump A.,(See Fig.0451) | 1 |
| DK***30 | Bearing,Roller | 2 |
| DK***00 | Camshaft | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#23193-36093)
| 61***40 | Injection Pump A.,(See Fig.0451b) | 1 |
| ND***50 | Ring,Adjust | 1 |
| ND***80 | O-Ring | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#36094-)
| 61***41 | Injection Pump A | 1 |
| ND***50 | Ring,Adjust | 1 |
| ND***80 | O-Ring | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping
| 01***75 | Bolt,(See Fig.0142) | 4 |
| 01***30 | Bolt | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump Linkage
| 01***20 | Screw | 3 |
| 01***06 | Nut,(With Back-Up Alarm) (Op), Nut; Was 01580-10806 | 3 |
| 01***09 | Nut (Itl) | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Pipe(#10001-23192)
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Pipe(#23193-)
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : S6d125-1e(S/N 10001-Up) : Fuel System : Water Separator And Piping
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
| 04***11 | Clip,See Fig. K4010-04a0 | 1 |
Kit
Komatsu : S6d125-1e(S/N 10001-Up) : Kit : Gasket Kit
| 02***43 | O-Ring,Water Manifold | 10 |
| 06***03 | Seal,Bearing (K2) | 2 |
| 07***20 | O-Ring,Relief Valve | 1 |
Lubricating Oil System
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Cooler
| 01***25 | Bolt,Without Revolution Sensor | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 12 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Filter And Mounting
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 7 |
| 02***14 | Plug (Heater Not Installed) | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Filter Piping
| 01***16 | Washer,Radio Controlled Slag Handling | 7 |
| 04***12 | Ring, Snap | 1 |
| 07***25 | O-Ring,Corrosion Resistor | 1 |
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe
| 01***25 | Bolt,(Without Auto Priming System) | 4 |
| 01***20 | Bolt,(Large Capacity Type) (Std) | 2 |
| 01***25 | Bolt,(Sandy? Dusty Terrain Spec.) | 5 |
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Torque Converter Oil Cooler
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 3 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 3 |
Komatsu : S6d125-1e(S/N 10001-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping
| 01***20 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Mechanical Governor) | 2 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 2 |
S6D125-1E(S/N 10001-UP) serial number reference
The engine serial plate is riveted to the engine block, typically on the left side near the injection pump or on the valve cover. The prefix is the alphanumeric model code (e.g., S6D125-1E) stamped on the plate, distinct from the machine chassis serial number.
| Prefix | Identifies | Notes |
|---|---|---|
| S6D125-1E | S6D125-1E | Engine model designation for the S/N 10001-UP range. Identified in factory parts catalogs and service manuals for the Komatsu 125 series. Variants include S6D125-1E-FA. Verify with your dealer for specific application mapping (e.g., D65, WA470). Single-source confirmation per published references catalog listings; confirm with dealer. |
Frequently asked questions
What is the engine type and configuration?
The S6D125-1E is a 6-cylinder, inline, turbocharged, aftercooled diesel engine with wet cylinder liners and mechanical fuel injection. It produces approximately 275 hp (205 kW) and 1,010 lb-ft (1,370 Nm) of torque.
What is the operating weight of the machine?
Operating weight varies by configuration and attachment. For example, the PC400-5 excavator ranges from approximately 38,000 to 42,000 lb (17,236 to 19,051 kg), while the D65E-12 dozer weighs around 69,000 to 73,000 lb (31,300 to 33,110 kg) depending on the undercarriage and counterweight.
What engine replaced the S6D125-1E?
The S6D125-1E was succeeded by the S6D125-2 and SAA6D125-2 series engines. These later models introduced electronic control units (ECM) and were designed to meet stricter emissions standards, such as Tier 4 Final and EU Stage V.
What S6D125-1E(S/N 10001-UP) owners discuss
What are the known powertrain and hydraulic behaviors for the Komatsu S6D125-1E engine series?
The S6D125-1E is a turbocharged and aftercooled diesel engine producing 275 horsepower (205 kilowatts) with 1,010 pound-feet (1,370 Newton meters) of torque. It is designed for heavy-duty applications such as excavators, bulldozers, and wheel loaders. The engine delivers high torque at low speeds. Community consensus indicates that Komatsu engines in this class are robust and fuel-efficient, but the hydraulic system is closely tied to engine performance; if the engine drops heavily in RPM under hydraulic load, the hydraulic system may be placing excessive load on the engine or the engine may be unable to produce expected power. Conversely, if engine speed remains normal but movements become weak, the hydraulic system is the primary suspect. The engine uses wet cylinder liners in direct contact with coolant. Typical failure points on the powertrain include worn steering-clutch and brake linings, contamination-driven wear in splash-lubricated final drive gear sets, and leaks at the hydraulic control-valve assembly that also serves as the tank. The pump flow settings differ from related Cummins-based units; for the S6D125-1E, the TVC is typically set halfway between the minimum and maximum, whereas Cummins-equipped machines often have the TVC set near the maximum. This reflects a different torque curve, with the S6D125-1E likely having maximum torque at a lower speed than the L10/Cummins variants.
What undercarriage or wear patterns are typical for machines equipped with this engine?
Machines powered by the S6D125-1E, such as the PC400-5 and D65 series, exhibit standard heavy-equipment wear patterns. Undercarriage wear on sprockets, links, and rollers is a primary maintenance concern. The line is generally designed to wear out complete machines all at once rather than individual components failing in isolation. If a hydraulic pump fails, the engine is often not far behind due to the high loads placed on the powertrain. Owners note that Komatsu parts, particularly undercarriage components, are expensive compared to aftermarket alternatives. Steering clutch and brake operation in both directions under load should be checked regularly, as wear here affects machine control. In dusty environments, air cleaner service intervals must be shortened to protect the engine and associated powertrain components.
What are the specific engine quirks for the S6D125-1E series?
The S6D125-1E is a naturally aspirated mechanical engine in its base configuration, meaning it has no electronic cold-start assist beyond glow plugs or ether aids. In cold conditions, coolant concentration and battery capacity must be checked closely. The engine uses hardened liners matched to the rings, and Komatsu like other manufacturers uses these to prevent wear issues common in other brands. However, the engine is sensitive to coolant maintenance. Letting the supplemental coolant additive deplete allows the wet liners to pit from cavitation. This pitting eventually shows up as coolant leaking into the crankcase, indicated by steam off the breather on startup and milky oil. The engine is known for running long with decent maintenance, often breaking due to external component failure rather than internal wear-out. It is distinct from the S6D102 series, which were Cummins-built or licensed Cummins engines; the S6D125 is a Komatsu-designed engine.
What are the common electrical or sensor issues associated with this engine?
Komatsu excavators and dozers equipped with this engine rely heavily on electronic control systems. A single faulty sensor or unstable power supply can trigger multiple warning signals. Owners often report intermittent starting, dashboard failure, or machines that randomly shut down. These issues are not necessarily engine mechanical failures but rather symptoms of electrical instability. If the machine suddenly derates, the exact warning and codes must be checked, as they may point to engine or aftertreatment diagnostics rather than hydraulic or mechanical faults. Monitoring oil pressure, coolant temperature, torque-converter oil temperature, and charge-pressure gauges at every start is recommended to log trends before a lamp trips.
What should be checked when buying a used machine with the S6D125-1E(S/N 10001-UP) engine?
When inspecting a used machine with the S6D125-1E(S/N 10001-UP) engine, check the following: 1. Coolant and oil condition: Look for an oil sheen in the coolant or milkiness/coolant smell in the oil, indicating liner pitting and coolant leakage into the crankcase. 2. Breather: Check for excessive steam off the breather on startup. 3. Undercarriage: Assess wear percentage on sprockets, links, and rollers. 4. Steering and brakes: Test steering clutch and brake operation in both directions under load. 5. Hydraulic system: Check for pump output and blade/tilt cylinder drift. 6. Engine performance: Verify compression or blow-by across all cylinders. 7. Filters and fluids: Ensure the supplemental coolant additive has been maintained. 8. Electrical: Check for intermittent starting or dashboard failures. 9. Air intake: Inspect the radiator core and charge-air hoses for debris or damage. 10. Serial verification: Confirm the engine serial number matches the S6D125-1E specification, as this engine replaced the M11 Cummins in units from serial A82000 and up due to the previous engine being overpowered by the advanced hydraulic system.
What are the recommended fluid specifications for the S6D125-1E engine?
For the S6D125-1E engine, use Komatsu Genuine Diesel Engine Oil meeting Komatsu Engineering Standard. For the hydraulic system, use Komatsu Hydraulic Oil HO56 (ISO VG46) or equivalent. For the final drive and transmission, use Komatsu Powertrain Oil TO10 (SAE 10W) or TO30 (SAE 30) depending on climate. Axle oil should be Komatsu Axle Oil AXO80 (SAE 80WZF). Coolant should be Komatsu Super Coolant AF-NAC. Always verify the exact specification against the machine's operation and maintenance manual, as requirements can vary by configuration and series.
How does the S6D125-1E differ from the S6D102 series in terms of application and reliability?
The S6D125-1E is a Komatsu-designed engine, whereas the S6D102 series were Cummins-built or licensed Cummins engines. The S6D125-1E was introduced to replace the M11 Cummins in units from serial A82000 and up because the M11 was overpowered by the advanced hydraulic system, leading to major valve train damage. The S6D125-1E provides more horsepower and a torque curve suited to the hydraulic load. Community consensus suggests that Komatsu engines like the S6D125-1E are more durable than the Cummins units they replaced, with fewer issues like piston ring slobbering. The S6D125-1E is known for running long with decent maintenance, while the Cummins units often required major overhauls every 6,000 hours or less. The S6D125-1E is not a disguised Cummins engine but a distinct Komatsu design with its own maintenance requirements, such as the critical need for supplemental coolant additive to prevent liner pitting.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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