Case Studies 02

CASE STUDY: 02
Skoda Kushaq 1.5 TSI (EA211 EVO) – Overheating With No Radiator Fan Operation

  1. Vehicle Details

    • Make / Model: Skoda Kushaq
    • Engine: 1.5 TSI (EA211 EVO, petrol)
    • Transmission: Automatic (DSG)
    • Model Year: 2021
    • VIN: MEXKRGPA4MG011545
    • Odometer: ~48,000 km
    • Market: India (MQB-A0-IN platform)
    1. Customer Complaint

    The customer reported that the vehicle was overheating during normal driving. The complaint was intermittent initially but became more frequent over time.

    Key observations by the customer:

    • Engine temperature warning tendency
    • Radiator fan not operating as expected
    • No drivability issues apart from overheating
    1. Initial Observations at Workshop

    Physical Checks

    • Coolant level: Normal
    • Engine oil level: Normal
    • No visible coolant leaks
    • Air filter: Recently replaced

    Temperature Behaviour

    • Instrument cluster temperature gauge remained steady at 90°C
    • Scan tool (Launch X431) showed actual coolant temperature reaching ~110°C

    Important Note: On VAG vehicles, the cluster gauge is intentionally damped and shows 90°C across a wide actual temperature range. The scanner reading reflects true coolant temperature.

    1. Critical Functional Symptoms
    1. Radiator fan does not switch ON, even at ~110°C coolant temperature.
    2. Radiator fan operates normally when AC is switched ON, but stops immediately when AC is turned OFF.
    3. Upper radiator hose becomes extremely hot.
    4. Lower radiator hose remains completely cold.
    5. No fault codes (DTCs) stored in ECU.

    These observations became the key diagnostic indicators.

    1. Diagnostic Reasoning

    Understanding VAG Cooling Logic

    On MQB / MQB-A0 platforms:

    • Radiator fan activation is not based on engine temperature alone.
    • ECU evaluates:
      • Engine coolant temperature (G62)
      • Radiator outlet temperature (G83)
      • Calculated heat rejection

    If coolant does not flow through the radiator, the ECU will not request fan operation, because the fan would be ineffective.

    Interpretation of Hose Temperatures

    • Hot upper hose + cold lower hose = coolant not reaching the radiator
    • This points directly to thermostat not opening

    Why Fan Worked With AC ON

    • AC system forces fan operation based on condenser pressure
    • This bypasses engine thermal logic
    • Therefore, fan operation with AC ON confirmed:
      • Fan motor OK
      • Fan control OK
      • ECU capable of commanding fan
    1. Suspected Root Cause

    Electronically controlled thermostat (coolant regulator) stuck closed

    Key points:

    • EA211 EVO uses a wax-type mechanical thermostat with electrical heating assistance
    • No position sensor is used
    • ECU infers thermostat operation purely from temperature behaviour
    • Mechanical failure of wax element does not generate a DTC
    1. Component Identification
    • Component: Water pump with integrated coolant regulator (thermostat)
    • Typical OE Part Family: 05E 121 111 (suffix varies by VIN)
    • Design:
      • Mechanical wax thermostat (fail-safe)
      • Electrical heating element (PWM-controlled)
      • No position feedback sensor
      • 5-pin electrical connector for power, ground, and diagnostics
    1. Repair Procedure Summary

    Removal & Replacement

    • Engine allowed to cool completely
    • Battery negative terminal disconnected
    • Coolant partially drained
    • Thermostat / water pump module removed
    • New module installed with new O-ring
    • Correct torque applied (plastic housing precautions)

    Coolant Filling

    • Vacuum filling machine used to evacuate air
    • Coolant drawn in under vacuum
    • Heater temperature set to HOT
    • Engine OFF during vacuum filling

    Vacuum filling is strongly recommended for EA211 EVO to prevent air locks.

    1. Post-Repair Verification

    After replacement and correct bleeding:

    • Upper hose heats normally
    • Lower hose warms once thermostat opens
    • Coolant temperature stabilises within normal range
    • Radiator fan now operates normally without AC
    • No overheating observed
    • Vehicle performs normally under all driving conditions
    1. Technical Deep Dive (Key Learnings)

    Thermostat Electrical Control (Overview)

    • ECU does not control thermostat position
    • ECU controls heating energy using PWM
    • PWM duty varies with:
      • Engine load
      • Coolant temperature
      • Predicted heat generation

    Why No Fault Code Was Logged

    • Heater coil electrically healthy
    • ECU plausibility checks passed
    • Mechanical wax element failed internally
    • Failure was thermal, not electrical
    1. Final Diagnosis

    Root Cause Confirmed: Mechanically stuck thermostat (coolant regulator) preventing coolant flow to radiator.

    Repair Outcome: Complete resolution of overheating after thermostat replacement and proper vacuum bleeding.

    1. Workshop Takeaway

    This case highlights an important principle for modern VAG engines:

    Always diagnose coolant flow first.

    • Fan behaviour alone is not a reliable indicator
    • Absence of fault codes does not rule out mechanical failure
    • Physical checks (hose temperatures) remain critical

    End of Case Study

    (This document is intended for technical reference and training use on passenger vehicles equipped with EA211 EVO engines.)

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