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It is important to realize that is a thermostatically controlled recirculating cooling system. Water from the pump goes through the powerhead and is then presented to the thermostat. If the thermostat says it is too cool, it is directed back to the water pump for recirculation.
But a bit is bypassed to keep the exhaust cool. That is the light spray you see when it is not at operating temp. When it is warm enough, the ‘stat opens and more water is discharged, resulting in a heavier spray. This process goes on constantly, with the ‘stat opening or closing as necessary. So, you will see varying amounts of spray being discharged. In fact, at slow speeds in cold water, it may be in recirculating mode all the time.