🚗 Classic Fault — Mercedes-Benz W115 (1968–1976)
Heater matrix blockage — no heat output
💰 Estimated Repair Cost
$80 – $300 USD
Parts and labour estimate
🔧 Tools Required
Drain pan, hose clamps
📋 Overview
The heater matrix gradually blocks with scale and corrosion from neglected coolant changes. Little or no heat output despite the engine at correct temperature.
🩺 Symptoms
- Little or no heat from heater
- one hose hot, other warm or cold
- heater better with engine revved
🔍 Possible Causes
- Blocked heater matrix
- air lock in heater circuit
- stuck heater valve
🛠️ Diagnosis Steps
Check both heater hoses with engine warm — both should be hot. Cold return hose confirms matrix blockage.
✅ Most Confirmed Fix
Flush matrix with reverse flow. If not recoverable, replace matrix — requires dashboard removal.
65% of users confirm this fix worked (12 reports)
🏷️ Parts Needed
Heater matrix for W115; coolant flush solution
🔗 Other Mercedes-Benz W115 Faults
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