The reason I am saying too high flow through the radiator is the following info I have:
My wife's car is a VW CTi ( the South African guys will know what car this is). It is a reproduction basically of the old 70's VW Gti Mk1 with the 1800 injected engine. Well, anyway, it's radiator got a crack and I needed to replace it with a new one. Upon removal and fitment of the radiator I noticed the core consist of pipes that are something like 10mm in diameter each. Comparing this to the fine piped core of the datsun and even my Nissan car, I would say that nissans have a thin piped core to slow down flow through the core because as we all know, water flows very slow through a straw compared to a garden hose.
That is why I lean in the direction of too fast flow.