Pontiac Engine Cooling COOLING SYSTEM CIRCULATION . Pontiac cooling system uses reverse flow circulation for maximum cooling efficiency. In reverse flow, cooled water from the radiator passes first to the cylinder heads, which are the hottest parts of the engine, and then to the cylinder block which is the coolest portion of the engine. Pontiac Engine Cooling System Upgrade - High Performance Jan 01, 2009Reducing Engine Operating Temperature With A Pulley Swap And An Evans Cooling System Upgrade. Many Pontiac owners just accept the fact that a high-horsepower engine is going to run hot on the street.