Cooling System Inadequacy
Symptoms
Engine overheating, particularly in traffic or on hot days. The temperature gauge climbs steadily, coolant may boil over, and in extreme cases the engine suffers heat-related damage (warped housings, blown coolant seals).
Cause
Rotary engines generate more waste heat than reciprocating engines of equivalent power. The Cosmo Sport's cooling system was designed for 1960s Japanese conditions and 1960s driving patterns (lower speeds, cooler ambient temperatures). In Australian summer conditions, the original radiator, water pump, and fan setup are marginal. After 50+ years of corrosion and degradation, they are often inadequate.
Fix
Flush and inspect the entire cooling system.
Replace the thermostat.
Consider an upgraded aluminium radiator (available from specialist fabricators, there is no off-the-shelf item for the Cosmo Sport).
Ensure the water pump is functioning efficiently.
An electric fan conversion can provide better airflow at low speeds than the mechanical fan.
Always use quality coolant at the correct concentration.
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