Komatsu D31P-20 Radiator Flush

[MikePhua]

The Komatsu D31P-20 is a compact utility dozer powered by the Komatsu S4D102E turbocharged diesel (≈70 hp) and carries a cooling-system capacity of about 5.8–6.0 US gallons (22 l). Flushing the radiator and cooling circuit is a routine but safety-critical service that keeps engine temperatures stable, prevents corrosion and cavitation, and prolongs water-pump and head gasket life. Always follow the machine’s service manual and your Komatsu distributor’s guidance for chemicals and anti-corrosion treatments.
Why flush the cooling system

• Removes scale, sediment and biological growth that reduce heat transfer and block passages.
  
• Eliminates contaminated or degraded coolant whose inhibitors have expired.
  
• Prevents localized overheating, which can cause head warpage or premature water-pump failure.
  
• Restores proper freeze/boil protection and corrosion inhibition for the alloy materials used in the engine and radiator.
  

Key parameters to know before you start

• Cooling system capacity: ~5.8–6.0 US gallons (22 L).
  
• Engine family: Komatsu S4D102E (service intervals and specs vary by serial).
  
• Tools suggested: catch pan, air pressure or garden-hose backflush kit, chemistry-safe flush pump, torque wrenches, PPE (chemical goggles, gloves), temperature gun.
  
• Safety constraint: never remove the radiator cap while hot; follow the manual’s safety steps (blocking tracks, locking out machine, etc.).
  

Safe, recommended flushing approach (practical sequence)

• Prepare and secure: park on level ground, block tracks, stop engine and allow engine to cool to ambient. Put on PPE and have absorbent pads and a waste-coolant container ready.
  
• Drain old coolant: open radiator drain(s) and engine block drain (if equipped). Collect used coolant for proper disposal per local regs. Note approximate drained volume to confirm capacity.
  
• Inspect and clean externals: check fan belt tension, radiator fins and screen for external clogging (plant material, dust); remove debris and straighten fins before reassembly.
  
• Backflush the circuit: with drains closed, introduce clean water (or a manufacturer-approved neutral radiator cleaner) at the filler and force water through the system in the reverse flow direction (use low-pressure garden hose or dedicated backflush kit). Repeat until drained water runs clear. Avoid high pressure that can damage hoses, cores or seals.
  
• Optional chemical clean: if heavy scale or oil contamination exists, use a commercially available radiator flush/cleaner formulated for diesel engines and compatible with aluminum and cast-iron components. Follow product directions exactly and flush thoroughly with water afterward. Avoid strong acids or household chemicals unless explicitly approved by the OEM.
  
• Add corrosion inhibitor and coolant: the Komatsu manual references use of approved anti-corrosive agents (example: KI-2 type references in service literature) and states to select amounts to match water quality — contact your Komatsu distributor when in doubt. Refill with the correct diesel/engine coolant mix and top to specified level.
  
• Bleed air and verify: run engine to normal operating temperature, cycle heater and any valves, re-check coolant level, inspect for leaks, and re-bleed air until level stabilizes. Re-check fan belts and hose clamps after a short test-run.
  

What NOT to do (important safety and longevity notes)

• Do not remove radiator cap while the engine is hot — hot coolant can spurt and cause severe burns.
  
• Avoid improvised aggressive mixes. A decades-old forum post describes a backflush recipe using muriatic acid and formaldehyde; such mixes are hazardous (toxic fumes, severe corrosion risk, damage to rubber/plastic and aluminum parts) and are not an OEM-recommended procedure. Use only approved cleaners and follow Komatsu’s manual or distributor advice. If heavy contamination persists, consult a professional shop or Komatsu service.
  

Troubleshooting tips & inspection checklist

• If coolant is oily or foamy → suspect oil cooler leak (internal) or head gasket issue — stop and diagnose before simply flushing.
  
• If heater works poorly or overheating reoccurs → check thermostat operation, water-pump condition and radiator core for internal blockage.
  
• If repeated re-contamination happens → inspect intake water sources (if top-up water is used), tank/surge contamination, or make-up water quality (use distilled or properly treated water).
  
• Record: date, hours, drained volume, type/brand of coolant and corrosion inhibitor used — good records help diagnose future problems.
  

Suggested intervals and economics

• Typical practice for machines of this class is to inspect coolant condition at every major service interval and replace coolant or perform a full flush per manufacturer interval (often every 1–2 years or as service manual specifies depending on coolant type and duty). Using proper inhibitors extends the life of coolant and parts, reducing total cost of ownership. Consult the D31P-20 manual for the exact interval matched to coolant chemistry.
  

Parts, materials and compatibility notes

• Use replacement hoses, clamps and thermostat assemblies that meet Komatsu part numbers for D31P-20 where possible; radiator cores and water-pump bearings wear over time and will reduce cooling efficiency if not serviced. Have spares for clamps and seals when reassembling.
  

Short technical glossary (terms used above)

• Backflush — forcing clean fluid through the cooling passages opposite the normal flow to dislodge debris.
  
• Corrosion inhibitor — chemical additive that prevents oxidation and electrochemical corrosion in the cooling circuit.
  
• Radiator core — the finned tubes where heat is transferred from coolant to air; easily clogged by external debris.
  
• KI-2 — an example referenced in Komatsu literature as an anti-corrosive treatment class; quantities should follow distributor guidance.
  

Context and brief manufacturer background
Komatsu is a century-old Japanese manufacturer founded in 1921 and is one of the world’s largest construction-equipment makers; the D31 family is a long-running compact dozer line known for utility tasks in construction and farming. Parts, manuals and serial-specific procedures are available through Komatsu distributors and official service literature — using those sources reduces risk and protects machine resale value.
Practical corner stories

• A regional contractor who ignored a slow-flowing radiator core replaced coolant twice per season; after a proper backflush and core cleaning the cooling temperature dropped 8–10°C under identical loads, and fuel economy slightly improved due to reduced thermal stress.
  
• An owner reported catastrophic aluminum corrosion after using a strong acid flush from an online recipe: the radiator and several hose fittings required replacement. After that, they switched to OEM-approved cleaners and scheduled yearly checks. (These anecdotes illustrate why OEM guidance matters.)
  

Final recommendations

• Always consult the Komatsu D31P-20 service manual and your local Komatsu distributor before using chemicals or non-standard procedures.
  
• Prefer neutral, engine-safe radiator cleaners and thorough water backflush rather than aggressive household acids.
  
• Keep records of coolant chemistry and service actions; if in doubt, let a trained service technician inspect the core, water pump and oil-cooler interface before returning the machine to heavy duty.