🚗 Classic Fault — Mercedes-Benz W115 (1968–1976)
Overheating on sustained highway driving
💰 Estimated Repair Cost
$20 – $120 USD
Parts and labour estimate
🔧 Tools Required
Drain pan, hose clamp pliers, multimeter
📋 Overview
Temperature gauge climbs toward the red on sustained highway speeds above 100 km/h. The W115 cooling system is adequate when in good condition but requires all components to function correctly.
🩺 Symptoms
- Temperature gauge rising at highway speed
- normal temperature in town
- coolant overflow
- steam from under bonnet in severe cases
🔍 Possible Causes
- Thermostat stuck partially closed
- restricted or scaled radiator
- faulty water pump impeller
- air locks in coolant system
- incorrect coolant mixture
🛠️ Diagnosis Steps
- Check thermostat opens at 80C.
- Check radiator flow — flush if scaled.
- Inspect water pump for correct impeller.
- Bleed cooling system for air locks.
- Check coolant mixture 50/
✅ Most Confirmed Fix
Replace thermostat. Flush and refill coolant system. Replace water pump impeller if plastic.
72% of users confirm this fix worked (18 reports)
🏷️ Parts Needed
Wahler or Behr thermostat 80C; water pump
🩺 Related Symptoms
🔗 Other Mercedes-Benz W115 Faults
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