Komatsuengine(no series)

Komatsu S6D125-1EE(S/N 10001-UP)

Maintenance schedule, common problems & OEM parts breakdown

The Komatsu S6D125-1EE (S/N 10001-UP) is a 6-cylinder, turbocharged, aftercooled diesel engine belonging to the 125-series family. It delivers approximately 275 hp (205 kW) and 1,010 lb-ft (1,370 Nm) of torque. This engine powers mid-to-heavy class Komatsu equipment, including the D65E-12 and D65PX-12 crawler dozers, PC400-5 and PC400-6 excavators, and WA470-3 wheel loaders. Production spans from the mid-1990s through the early 2000s, with an operating weight range for these machines typically between 35,000 and 80,000 lb (15,876 to 36,287 kg). It succeeded earlier naturally aspirated 6D125 variants and was later replaced by electronically controlled S6D125E-2 and SAA6D125E-2 engines in the D65EX-15 and PC400-7 generations.

The S6D125-1EE marks a transition in the 125-series lineage, introducing forced induction to the base chassis variants while retaining the robust mechanical fuel injection and wet liner architecture of the 6D125. Its significance in the used and parts market stems from its widespread installation across high-volume PC400 and D65 platforms. The engine's mechanical simplicity and lack of complex electronic emissions controls make it a preferred candidate for remanufacturing and long-term fleet maintenance. The large installed base ensures that aftermarket support for critical components like pistons, cylinder liners, and turbochargers remains robust and cost-effective.

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 S6D125-1EE(S/N 10001-UP) specifications

Engine

ModelS6D125-1EE (S/N 10001-UP)
Type4-cycle, water-cooled, inline vertical, direct injection, turbocharged and aftercooled
Displacement11 liters
Cylinders6
Gross Power202 kW (275 hp)
Net Power180 hp (134 kW)
Torque1,370 N·m (1,010 lbf·ft)
Emissions TierNot documented for this exact serial range — verify with your dealer

Weights

Operating WeightNot documented for this exact serial range — verify with your dealer
Shipping WeightNot documented for this exact serial range — verify with your dealer
Ground PressureNot documented for this exact serial range — verify with your dealer

Dimensions

Transport LengthNot documented for this exact serial range — verify with your dealer
Transport WidthNot documented for this exact serial range — verify with your dealer
Transport HeightNot documented for this exact serial range — verify with your dealer
Track GaugeNot documented for this exact serial range — verify with your dealer
Ground ClearanceNot documented for this exact serial range — verify with your dealer

Performance

Travel SpeedNot documented for this exact serial range — verify with your dealer
GradeabilityNot documented for this exact serial range — verify with your dealer

Service capacities (summary)

Fuel TankNot documented for this exact serial range — verify with your dealer
Hydraulic SystemNot documented for this exact serial range — verify with your dealer
Engine OilNot documented for this exact serial range — verify with your dealer
Cooling SystemNot 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.

Komatsu S6D125-1EE(S/N 10001-UP) maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil level and condition
  • Check hydraulic fluid level via sight glass
  • Check coolant level and ensure cap is secure
  • Drain water from fuel separator
  • Check DEF level on Tier 4 machines
  • Check air filter restriction indicator
Every 250 h
  • Change engine oil and filter
  • Grease all points (boom, stick, bucket, swing bearing)
  • Check fluid levels
  • Inspect air filter element
  • Inspect belts and hoses
  • Perform visual walk-around inspection
Every 500 h
  • Change engine oil and filter
  • Replace fuel filter
  • Replace hydraulic return filter
  • Test battery and alternator
  • Test coolant SCA
  • Collect KOWA oil sample
Every 1,000 h
  • Change engine oil and filter
  • Replace air filter outer element
  • Change final drive oil
  • Inspect turbocharger
  • Check valve adjustment
  • Inspect structural welds
Every 2,000 h
  • Change engine oil and filter
  • Change hydraulic oil
  • Flush and replace coolant
  • Service transmission
  • Comprehensive component evaluation
  • Inspect undercarriage wear

Servicing the S6D125-1EE(S/N 10001-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

Monitor KOWA oil analysis results at every 500-hour interval to detect early wear metals in the splash-lubricated steering-clutch case and final drives. These systems lack independent filtration, making fluid cleanliness critical. Track coolant pH and SCA concentration closely; the S6D125-1EE uses wet cylinder liners that are highly susceptible to cavitation pitting if supplemental coolant additive depletes. A drop in SCA levels often precedes coolant leakage into the crankcase. Log trends in charge pressure and turbocharger boost to identify airflow restrictions before power loss occurs.

Corrective & Common Repairs

Address milky oil or steam from the breather on startup as immediate signs of coolant intrusion into the crankcase, usually caused by liner pitting or head gasket failure. Inspect the oil cooler element for internal cross-contamination between engine oil and coolant. Check the mechanical fuel injection pump for wear on the rack and governor linkage, which can cause erratic idle or loss of power. Verify the condition of the turbocharger shaft play and seal integrity, as excessive blow-by can accelerate oil degradation and reduce boost pressure.

Overhaul & Rebuild Points

Plan for an inframe overhaul when compression drops below specification or oil consumption exceeds limits, typically around 10,000 to 15,000 hours. Replace wet cylinder liners, pistons, and piston rings as a set to ensure proper sealing and heat transfer. Inspect the crankshaft for journal wear and replace main and rod bearings if clearance exceeds factory tolerances. During rebuild, replace the water pump, thermostat, and all engine seals to prevent post-repair leaks. Verify turbocharger housing cracks and impeller balance before reassembly.

Seasonal & Environment Servicing

In cold climates, verify coolant concentration and battery capacity before startup, as this mechanically governed engine lacks electronic cold-start assist beyond glow plugs or ether aids. In hot, dusty environments, shorten air cleaner service intervals and keep the radiator core and oil cooler fins clear of debris to prevent overheating. Monitor engine oil viscosity changes in extreme temperatures; use Komatsu EO or equivalent heavy-duty diesel oil rated for the ambient conditions. Ensure the fan belt tension is correct to maintain adequate cooling fan speed in high-heat applications.

S6D125-1EE(S/N 10001-UP) common service parts

Part numberPart
07281-00197Clamp,(With Pre-Fuel Filter)Check fitment →
ND092220-0040Filter,FuelCheck fitment →
6125-81-7032Element Ass'Y,Air CleanerCheck fitment →
600-181-4300Element Ass'Y,OuterCheck fitment →
ND090438-0420Shim? 1.9mm,Element HolderCheck fitment →

Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.

S6D125-1EE(S/N 10001-UP) fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CA115Engine crankshaft speed sensor and backup speed sensor failureFaulty speed sensor, broken wiring harness, or corroded connector at the pin interfaceReplace the speed sensor and verify voltage at the pin connector
CA111Internal engine controller faultElectronic Control Module (ECM) internal failureReplace or reprogram the ECM
CA451Common rail pressure sensor feedback value too highMalfunctioning rail pressure sensor or actual overpressure condition in the fuel systemDiagnose the fuel rail pressure sensor and check pump lines
CA452Common rail pressure sensor feedback value too lowFaulty rail pressure sensor or low fuel pressure supplyDiagnose the fuel rail pressure sensor and check pump lines
CA122Intake air pressure sensor feedback voltage too highIntake pressure sensor malfunction or wiring issueVerify the intake pressure sensor and wiring
CA123Intake air pressure sensor feedback voltage too lowSensor short circuit or airflow restriction in the intake systemCheck for a sensor short or an airflow restriction
CA153Intake air temperature sensor feedback voltage too highIntake air temperature (IAT) sensor errorReplace or test the IAT sensor
CA154Intake air temperature sensor feedback voltage too lowIntake air temperature (IAT) sensor errorReplace or test the IAT sensor
CA234Engine overspeedThrottle calibration error, engine load cycle issue, or operator misuseVerify throttle calibration and engine load cycle
CA441Battery voltage too lowWeak battery, faulty alternator, or voltage regulator issueReplace the alternator or battery; check the voltage regulator

Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.

S6D125-1EE(S/N 10001-UP) attachments & work tools

Motor Grader Attachments

The S6D125-1EE engine is explicitly linked to the GD750A-1 motor grader in factory equipment guides. This machine class utilizes standard grading blades and ripper configurations typical for high-output grading applications.

Crawler Dozer Blades

The engine powers the D65E-12, D65P-12, D65EX-12, and D65PX-12 dozer series. These models are equipped with straight-tilt blades for standard gauge configurations and wide-gauge low-ground-pressure swamp configurations. Factory guarding options include ROPS cabs and canopies, which affect machine height specifications.

Crawler Excavator Buckets

The S6D125-1EE and related 125-series engines are used in the PC400-5, PC400-7, and PC400LC-5/8 excavator families. Typical work tools include standard digging buckets and trenching buckets sized for the 20-ton class capacity. Hydraulic kit arrangements vary by generation, requiring specific flow rates for the associated main control relief valves.

Wheel Loader Buckets

The WA470-3 and WA470-3A wheel loaders utilize this engine family. Standard work tools include general-purpose and rock buckets. The machine class typically features a quick-coupler system for bucket attachment, with hydraulic connections routed through the loader boom structure.

All S6D125-1EE(S/N 10001-UP) assemblies by section

Every catalogued assembly group for the Komatsu S6D125-1EE(S/N 10001-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Accessory
Komatsu : S6d125-1ee(S/N 10001-Up) : Accessory : Air Compressor And Piping
07***12Gasket,(Without Air Compressor Type) (K2)4
07***12Gasket,(Without Air Compressor Type) (K1)8
07***16Gasket,Air Compressor Piping2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Accessory : Air Compressor(#10001-38810)
61***10Air Compressor Ass'Y,(See Fig.0711)1
DK***20Connecting Rod A1
DK***00Spring,Delivery Valve1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Accessory : Air Compressor(#38811-)
Cooling System
Komatsu : S6d125-1ee(S/N 10001-Up) : Cooling System : Cooling Fan And Mounting
01***30Bolt,(For Quick Shift) (Mitsubishi)22
01***40Bolt, Mount Master Brake Cylinder2
01***95Bolt,(For 2nd Travel Speed) (Op)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cooling System : Cooling Fan And Mounting (Suction Fan Type)
01***30Bolt,(For Quick Shift) (Mitsubishi)16
01***40Bolt, Mount Master Brake Cylinder2
01***55Bolt, Mount Tube To Switch Pump6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cooling System : Corrosion Resistor And Piping
01***20Bolt,(For Quick Shift) (Mitsubishi)1
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***08Nut,(For Canvas Canopy?Head Guard)1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cooling System : Water Pump And Mounting
01***16Bolt (With Air Heater & Conditioner)6
01***30Bolt,(For Quick Shift) (Mitsubishi)2
01***35Bolt,(For Quick Shift) (Mitsubishi)2
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Cylinder Block
Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Camshaft
01***22Bolt2
04***25Key, Plain Woodruff1
04***12Ring,Snap (For Ripper)12
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Crankshaft
01***25Bolt,(Without Rops Guard? Canopy)6
01***30Screw1
01***35Screw5
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Cylinder Block
01***12Bolt,(Without Air Compressor Type)2
01***45Washer,(For Travel Motor) (Not Show)14
04***14Pin, Dowel2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Cylinder Block Cover
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***08Nut,(For Canvas Canopy?Head Guard)2
01***16Washer,Radio Controlled Slag Handling2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing
01***40Bolt,(Dust And Dirt Protection)2
01***50Bolt, Radiator To Frame6
01***70Bolt - Thrust Plate Mounting2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Front Cover And Gear
01***25Bolt,(Without Auto Priming System)6
01***60Screw1
01***20Bolt,(For Quick Shift) (Mitsubishi)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Oil Pan
01***16Bolt, Battery To Frame Ground Wire Attaching1
01***25Bolt,(For Canvas Canopy?Head Guard)31
01***30Bolt,(For Quick Shift) (Mitsubishi)7
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Piston And Connecting Rod
02***13Pin, Dowel2
04***18Ring, Snap12
61***31Piston Ring Ass'Y6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Power Take Off (1/2)
01***35Bolt, Bolt, Mount Tubes To Switch And Work Pumps6
01***40Bolt,(With Service Valve R.H.)6
01***45Bolt6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Block : Power Take Off (2/2)
01***20Bolt,(Sandy? Dusty Terrain Spec.)6
01***20Bolt,(For Quick Shift) (Mitsubishi)2
01***25Bolt,(For Canvas Canopy?Head Guard)12
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Cylinder Head
Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Air Cleaner And Connection
01***40Bolt,(Dust And Dirt Protection)2
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***30Bolt,(For Quick Shift) (Mitsubishi)4
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Air Intake Manifold
01***30Bolt,(For Quick Shift) (Mitsubishi)14
01***55Bolt, Mount Tube To Switch Pump2
01***00Bolt, Mount Back-Up Alarm2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Cylinder Head(#26751-)
04***20Pin,Dowel (Welded)2
61***30Sleeve,Holder1
61***20Cotter, Valve48
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Exhaust Manifold And Turbocharger
01***80Bolt, Mount Strainer Flange2
01***00Bolt (M10-1.50x100)18
01***45Screw4
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Muffler
01***40Bolt,(Dust And Dirt Protection)4
01***55Bolt,(For Suction? Reversible Fan)4
01***30Bolt,Radio Controlled Slag Handling4
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Rocker Arm And Housing
01***95Bolt,(For 2nd Travel Speed) (Op)2
01***08Nut,R.H. Thread12
01***16Washer,Radio Controlled Slag Handling42
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Rocker Arm Housing Cover
01***16Washer,Radio Controlled Slag Handling24
61***11Cover,Head? No.2?3?4?5?66
61***10Gasket,Cylinder Head Cover6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Cylinder Head : Turbocharger(#23599-)
61***10Turbocharger Ass'Y,(Ta4532)1
GA***60V-Band1
GA***52Center Housing A1
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Electrical System
Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Alternator (35a)
60***60Alternator A. (35a),(With Non Hardening Pulley)1
KD***57Bearing,Ball? Front1
KD***80Collar1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Alternator (50a)
60***30Alternator A. (50a),(With Non Hardening Pulley)1
SD***X0Pulley,Non Hardening1
SD***X0Coil Assembly1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Alternator And Mounting (35a)
01***90Bolt, Fan Mounting1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Alternator And Mounting (50a)
01***30Bolt,(For Quick Shift) (Mitsubishi)1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Starting Motor (11kw)
60***31Starting Motor Ass'Y,(11kw)1
SD***00Metal1
SD***60O-Ring2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Starting Motor (7.5kw)
60***30Starting Motor Ass'Y,(7.5kw)1
KD***20Magnetic Switch Assembly1
KD***40Spring,Spring4
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Starting Motor And Mounting (11kw)
01***16Bolt, Battery To Frame Ground Wire Attaching1
01***40Bolt,(With Center Guard)3
60***20Clip,(Large Capacity Type)1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Electrical System : Starting Motor And Mounting (7.5kw)
01***40Bolt,(With Center Guard)3
66***10Gasket,Starting Motor1
(6***0)Starting Motor Ass'Y,(7.5kw) (See Fig.A6210-B4a3)1
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Engine Kit
Komatsu : S6d125-1ee(S/N 10001-Up) : Engine Kit : Gasket Kit
01***23Washer,Lock (K5)1
02***43O-Ring,Water Manifold6
07***10O-Ring,(F4350-62a0 -5 ), O-Ring; Komatsu S/N 22***01 & Abv - Was 07000-02010, O-Ring; Was 07000-020101
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Fuel System
Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Filter And Piping
01***25Bolt,(For Canvas Canopy?Head Guard)6
01***08Nut,(For Canvas Canopy?Head Guard)2
01***16Washer,Radio Controlled Slag Handling2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)
ND***50Bolt1
ND***40Bolt2
ND***61Bolt6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)
ND***61Feed Pump Ass'Y1
ND***40Washer? 1mm,Plate1
ND***70Washer,Union4
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)
ND***40Plate,Thrust1
ND***40Plug,Screw1
ND***60Governor Ass'Y1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)
ND***20Washer? 1.0mm,Cover Plate2
ND***30Lever,Adjusting1
ND***70Packing,Rubber Plate1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)
61***50Injection Pump Ass'Y1
ND***50Ring,Adjust1
ND***80O-Ring1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)
ND***70O-Ring6
ND***71Rack,Control1
ND***50Seat,Spring? Lower6
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping
01***75Bolt,(See Fig.0142)4
01***30Bolt4
01***20Bolt,(For Quick Shift) (Mitsubishi)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Pipe(#23599-)
01***45Bolt, Divider Valve Mounting12
07***65O-Ring,Cylinder Block6
07***12Gasket,Mechanical Pump Piping2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Fuel System : Water Separator And Piping (Sandy And Dusty Spec.)
01***30Bolt,(For France Noise Suppression)2
01***70Bolt4
01***16Washer,Radio Controlled Slag Handling2
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Lubricating Oil System
Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Cooler
01***25Bolt,Without Revolution Sensor2
01***25Bolt,(For Canvas Canopy?Head Guard)12
01***65Bolt,(Except Japan)2
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Filter
01***25Bolt,(For Canvas Canopy?Head Guard)8
02***16Plug1
04***12Ring, Snap1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Piping
01***50Bolt,(With Service Valve R.H.)4
01***16Washer,Radio Controlled Slag Handling7
04***12Ring, Snap1
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe
01***25Bolt,(Without Auto Priming System)4
01***20Bolt,(Large Capacity Type) (Std)2
01***25Bolt,(Sandy? Dusty Terrain Spec.)5
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : P.T.O. Lubricating Oil Piping
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***40Bolt,(With Service Valve R.H.)1
07***12Gasket,(Without Air Compressor Type) (K2)23
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Torque Converter Cooler
01***20Bolt,(For Quick Shift) (Mitsubishi)11
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***30Bolt,(For Quick Shift) (Mitsubishi)3
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Komatsu : S6d125-1ee(S/N 10001-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping
01***20Bolt,(With Auto Emergency Steering)2
01***30Bolt,(For Mechanical Governor)2
01***16Bolt, Battery To Frame Ground Wire Attaching2
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S6D125-1EE(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 first portion of the engine model code (e.g., S6D125-1EE), not a separate 3-character PIN; the PIN is a 17-character ISO code found on the emissions/export plate. Read the engine model code directly from the plate to identify the series and generation.

PrefixIdentifies
S6D125-1EEEngine Model

Frequently asked questions

What is the engine type for the Komatsu S6D125-1EE?

It is a 6-cylinder, 4-stroke, water-cooled, turbocharged, and aftercooled diesel engine with a displacement of approximately 11 liters.

What is the operating weight of machines using this engine?

Operating weight varies by configuration and series, typically ranging from 15,876 to 36,287 kg (35,000 to 80,000 lb) for the D65 and PC400 class equipment.

What engine replaced the S6D125-1EE?

It was superseded by the electronically controlled, turbocharged S6D125E-2 and SAA6D125E-2 engines introduced in the D65EX-15 and PC400-7 generations.

What S6D125-1EE(S/N 10001-UP) owners discuss

What are the known powertrain and hydraulic behaviors for machines using the S6D125-1EE engine?
The S6D125-1EE is a turbocharged and aftercooled diesel engine paired with hydraulic systems requiring specific pressure settings; for example, the TVC (Torque Converter Valve Control) is set differently than on naturally aspirated variants, typically positioned between minimum and maximum limits rather than at the maximum. The engine delivers high torque at low speeds, beneficial for heavy-duty applications. Hydraulic performance should be monitored for temperature sensitivity; weakness when hot often indicates internal leakage in pumps, valves, or motors rather than pump failure alone. Shared hydraulic weakness across all functions points to supply, pump control, or engine performance issues, while single-function weakness points to circuit-specific components like cylinders or control valves.
What undercarriage or wear patterns are typical for this machine type?
Machines equipped with this engine, such as the GD750A-1 motor grader (S/N 10001-UP), feature specific track gauge and ground clearance dimensions. Standard track shoe width is 510 mm (20.1 in) for standard-gauge configurations and 950 mm (37.4 in) for wide-gauge/low-ground-pressure variants. Undercarriage wear patterns are influenced by ground pressure; wide-gauge configurations reduce ground pressure for swamp or soft terrain. Track tension and roller condition significantly affect travel speed and pulling behavior. If a machine pulls to one side, check for mud/debris packed into one undercarriage, roller condition, and track-chain wear before diagnosing hydraulic final drives. Track tension must be verified to prevent repeated loosening.
What are the engine quirks per the S6D125-1EE series?
The S6D125-1EE series uses wet cylinder liners in direct contact with coolant. Maintaining supplemental coolant additive (SCA) levels is critical to prevent liner pitting from cavitation, which can lead to coolant leaking into the crankcase. The engine is mechanically controlled and naturally aspirated in some base variants (6D125-1A), but the S6D125-1EE is turbocharged. It lacks electronic cold-start assist beyond glow plugs or ether aids, requiring close monitoring of coolant concentration and battery capacity in cold conditions. The engine is known for durability with hardened liners matched to rings, often outlasting Cummins-based variants in similar applications when maintained properly.
What are common electrical or sensor issues reported?
Komatsu machines with this engine family rely on electronic control systems where a single faulty sensor or unstable power supply can trigger multiple warning signals. Common issues include intermittent starting, dashboard failures, or random shutdowns. Operators should watch the oil pressure, coolant temperature, torque-converter oil temperature, and charge-pressure gauges at every start. Logging trends is preferred over waiting for caution lamps to trip. Multiple fault codes often point to battery state, engine/chassis grounds, or connector integrity rather than component failure.
What should be checked when buying a used machine with the S6D125-1EE (S/N 10001-UP)?
Verify the exact serial number against the engine identification guide to confirm the S6D125-1EE designation. Check for coolant contamination in the crankcase (milky oil or steam from the breather) as a sign of liner pitting due to depleted SCA. Inspect the radiator, hydraulic oil cooler, and charge-air cooler for debris packed between heat exchangers. Test hydraulic performance cold and hot to identify internal leakage. Check track tension, roller condition, and undercarriage wear. Verify battery capacity and ground connections. Ensure the TVC and pump flow settings match the specific engine variant, as settings differ between naturally aspirated and turbocharged models.
What fluid specifications are recommended for this engine?
Use Komatsu Genuine Diesel Engine Oil, Komatsu Hydraulic Oil, and Super-coolant AF-NAC. Specific fluid types include Komatsu EO, TO, AXO, and HO series fluids as appropriate for the system. Always consult the operation and maintenance manual for the exact capacity and specification grade, as requirements vary by configuration and series.
What is a safety-critical fix related to the cooling system?
Maintaining supplemental coolant additive (SCA) levels to prevent wet liner cavitation and subsequent coolant leakage into the crankcase. Have your dealer verify the SCA concentration and coolant system integrity.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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