No. From the engine specs, you know the horsepower at a specified RPM. You use this to find where your engine's curve should lie within the shaded area. Then, for that bhp, you know the heat load at all speeds. This inherently assumes that your car's curve really does lie within the shaded area.So, the graph from the physicsforum page isn't useful unless I know the bhp at each rpm right? Because that is the only way I could calculate the flowrate.
Once you know the heat load at the specified engine speed and bhp, you can measure the temperature change at that engine speed and back out the coolant rate. That will give you the proportionality constant between the coolant rate and the engine speed.