[M_a_t_t]

I've been reading Road Vehicle Aerodynamics by A.J. Scibor-Rylski (1st edition) on my lunch break at work recently. Today I read 'The idealised air cooling system' pg. 60-65. I have a few things I have been thinking about regarding this section but since it's 4am here I'm just gonna start with the simple question and get the rest out later.

This question might appear to be directed at JulianEdgar, but I don't intend it to. The more people looking at it the better.

He has suggested to measure cooling efficiency by taking pressure readings on both sides of the radiator (intercooler, etc) and comparing it to the pre-modified readings. If the difference is increased then the system is working better (based on memory, couldn't find the section in his book to cite it). The greater the pressure difference the higher the flow (and therefore speed for a given inlet opening). However, in Road vehicle aerodynamics it says you want slower flow for best heat dissipation. Which makes sense to me because of the longer time the air can absorb the heat from the radiator. So does the pressure measurement just simplify the required testing and provide adequate data? Or does this testing method need some revision? Or maybe I just need to read the section again.

I feel like I am missing something simple.