You are driving a fully laden articulated lorry down a long, steep gradient. The retarder has been active for several minutes and you notice it is becoming less effective. What is the most likely cause?
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AThe engine braking has automatically disengaged to protect the transmission
BThe air pressure reservoir feeding the retarder has depleted
CThe retarder oil has become overheated and lost viscosity
DThe retarder is designed to reduce effectiveness on prolonged descents as a safety feature
✓ Correct answer: C. The retarder oil has become overheated and lost viscosityRetarders (hydraulic or electromagnetic) generate heat when absorbing kinetic energy; prolonged use causes the fluid or components to overheat, reducing braking effectiveness — the driver should use lower gears and allow cooling rather than relying solely on the retarder.
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