Summary theory (short)
- The Hino Super F GH1H uses a thermostatic viscous fan clutch: a rotor attached to the fan is coupled to the drive hub through silicone viscous fluid inside a sealed chamber and a temperature‑sensing bimetal spring. At low coolant/air temperatures the clutch provides low coupling (fan freewheels); at high temperatures the bimetal spring moves a valve or changes clearance so fluid shear increases and the fan locks up, increasing airflow. Faults come from worn bearings, loss of silicone fluid, a failed bimetal element, or seizing — producing either overheating (insufficient coupling) or excessive fan drag/noise and fuel loss (stuck locked).

Ordered workshop procedure (theory + what you do, in order)
1. Safety and prep
- Work on a cold engine. Park on level ground, set parking brake, chock wheels.
- Disconnect negative battery terminal to avoid electric fan starting or accidental cranking.
- Wear eye/hand protection. Support the front if you need to get under the vehicle.
- Have a fan‑holding tool or heavy strap ready to prevent the fan from spinning/tipping when removing fasteners.

Why: prevents burns, accidental startup, and protects you from blade movement.

2. Confirm fault and document
- Note symptoms (overheat, high idle fan noise, whine, vibration, blown belts).
- Run stationary hot‑engine test: with cooling system at operating temperature observe fan behaviour — does it engage strongly when hot? Listen for bearing noise. At idle and higher RPM check change in fan speed.
- Basic checks: coolant level, thermostat operation, radiator condition, belt tension/pulley condition. Rule these out before clutch replacement.

Why: fan clutch faults mimic other cooling system faults — you must eliminate coolant/thermostat/radiator/belt causes.

3. Accessibility and protection
- Remove or loosen the fan shroud(s) and any obstructing cooling components to provide clearance (note shroud orientation).
- If required, loosen belts or remove the serpentine belt to allow safe removal of fan assembly without tension.

Why: prevents blade damage and allows safe removal; shroud condition affects airflow and can mimic clutch fault.

4. Support the fan and prepare to remove
- Use a fan‑holder tool on the clutch hub or support the fan with a strap against the radiator frame to take the load.
- Mark fan position relative to pump/hub if alignment matters.

Why: prevents the fan from turning and protects threads/bolts/your hands.

5. Remove fan clutch assembly
- Identify attachment: typically the clutch bolts to the water‑pump flange or is threaded on a hub. Use correct socket/wrench on the hub or nuts and remove in sequence.
- Remove the fan + clutch as an assembly if possible. Lift straight out, avoid bending blades.

Why: gaining access for inspection/bench testing and replacement.

6. Inspect components (visual + mechanical)
- Visual: check for silicone oil leakage (wetness/shine/oily residue between rotor and housing), cracked fins, bent blades, or corrosion.
- Bearing/wobble: hold hub and try to rock the fan; any axial or radial play indicates bearing wear.
- Runout: spin the fan by hand; listen/feel for roughness.
- Bimetal spring/thermostat: inspect for visible damage, corrosion or broken spring.

Why: determines root cause (bearing, fluid loss, bimetal failure, blade damage). Each defect maps to a different repair.

7. Bench test the clutch (theory + method)
- Cold free‑spin: with the clutch cold it should turn freely with moderate resistance (a couple of turns). If it’s locked solid = seized.
- Heat test: carefully apply heat to the bimetal area (heat gun/propane torch cautiously) while holding the hub; the clutch should progressively lock as the bimetal expands and increases fluid coupling. If it does not lock when hot, the thermostatic mechanism or fluid has failed. If it stays locked when cooled, it’s stuck.
- Bearing noise/wobble: any grinding or play fails the bearing test.

Why: verifies viscous coupling and thermostatic action — shows whether clutch will engage when engine is hot or not.

8. Decide repair vs replace
- Replace the entire clutch if you have leakage, bearing play/noise, failed heat test, or damage. Viscous clutches are normally replaced as complete units.
- Only replace seals or recondition if vendor documentation supports rebuilding; otherwise replacement is standard workshop practice.

Why: oil loss, bearing failure, or broken bimetal rarely reliably repaired in‑service; new unit restores correct hydraulic/thermal behavior.

9. Install new clutch
- Clean mating surfaces (water‑pump flange/hub) removing old gasket/sealer, corrosion, grease.
- Fit new clutch to fan if delivered separately; ensure correct orientation and that the bimetal element faces the airflow side per manufacturer instructions.
- Align marks and thread/bolts by hand; tighten in a star pattern if multiple bolts.
- Torque all fasteners to manufacturer specification (use Hino workshop torque values). If you don’t have the manual, tighten hand‑firm then final torque per spec; do not overtighten.
- Refit shroud and belts, set belt tension per spec.

Why: correct mounting ensures concentricity and prevents vibrations; correct torque retains clamping without damaging studs.

10. Reassembly checks
- Spin the fan by hand to check free movement and no rubbing on shroud.
- Reconnect battery.

11. Run and test
- Start engine, allow to reach operating temperature. Observe fan engagement as temperature rises: it should show increased coupling as engine warms (fan speed increase at idle or load).
- Drive/idle test: monitor coolant temperature, listen for bearing noise, check for improved response to load/climb.
- After initial run, shut down, recheck fan‑to‑shroud clearance and retorque fasteners if manufacturer recommends recheck after service interval.

Why: ensures the replacement has corrected coupling and removed previous symptoms; verifies no new issues.

How the repair fixes the typical faults (concise)
- Replacing a leaking clutch restores the viscous fluid volume and sealed chamber. That re‑establishes the shear coupling between hub and rotor so the fan will develop torque when the thermostatic element calls for it—preventing overheating caused by insufficient airflow.
- Replacing a clutch with worn bearings or warped rotor removes mechanical play/vibration and noise, protecting the water pump shaft and belt drive and eliminating wobble that reduced effective airflow.
- Replacing a clutch with a failed bimetal spring restores the thermal control (low drag when cold, full engagement when hot). That fixes faults where the fan is either permanently locked (excessive drag, fuel penalty, noise, high engine load) or permanently free (overheating).
- Correct installation (alignment, torque, shroud reassembly) ensures optimal airflow path and prevents blade rubbing or loss of cooling efficiency.

Quick troubleshooting mapping (one‑line)
- Overheats under load but fine cold → clutch not locking (loss of viscous coupling or failed bimetal).
- Fan noisy, high rpm all the time, poor fuel economy → clutch locked, stuck or bimetal permanently closed, or broken shroud causing high drag.
- Vibration/wobble → bearing or warped fan blades; replace assembly.
- Oily residue at clutch seam → internal fluid leak → replace clutch.

Final workshop reminders (short)
- Use OEM or equivalent quality clutch; viscous clutch specs vary by model.
- Always follow Hino torque and procedural specs where available.
- Inspect related items (water pump shaft, fan blades, shroud, belts, thermostat, coolant condition) as part of the repair to prevent repeat failures.

Done.
rteeqp73

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