I will ask all of you that say slow, how does the water pump in you car flow vs. engine load operation?
The water pump flow volume increases with engine RPM's of course. The thermostat may close a bit to throttle the flow if it gets too cold. If the radiator gets clogged then it shows up first by the engine running hotter at highway speeds. I imagine this is because there is less cooling area available as the radiator gets clogged rather than the flow being impeded. Does that sound right?
Correct Jeff. The pump output is low at idle, rises in a parabolic curve with RPM, as the max heat is generated at max power, which is at high RPM.
When working in Germany I learned that the Autobahn was not the worst case design case, it was easy due to the high flow of air through the radiator. Worst case was pulling a trailer on a hot day up a pass in the Alps. High heat generation, low flow of warm thin air. Made perfect sense. That coolant - air - has to carry the heat away.