Gday
looking at the fan on the radiator , size wise and location of it, id say it looks rather inefficient, it could also be a faulty temp sender, id get a hand held thermometer (lazer type) and measure both , bottom and top hoses, and go from there.

The fan fills the complete core, no way of fitting a bigger one, it is a Spal unit, do not think we get a better brand name in SA. It is also located in the middle of the motor.

Once the fan kicks in, the temp drops, it is the high way driving that is causing my problem, and this is were a fan is not needed.

Also installed a temp switch that switch on at 82 degrees and of at 68degrees last night, will check it out.

is there anything restricting airflow infront of the radiator?

On highway (freeway) driving the temp is not suppose to go high at all as there is sufficient wind that goes through the radiator.

This is really baffling me. I am trying to think what it can be but without us standing next to the car it is quite difficult to figure out.Is it possible that the water is circulating too fast when you are driving on the highway (freeway) with higher than city driving revs?

Only the stock datto grill infront of the rad.

1200GX, i'm also leaning in that direction, or pressure.
Will have a better overall view when I can see actual Temp readings.

With a fully pressurised system the motor can run up to 110C quiet safely and it is not overheating, above 120C start to worry.

im starting to think too much flow as well, it is a plausible effect from the cause. but that would mean the thermostat would be jamed open on the freeway, from the heat in the coolant.

If its jammed open just check if the water is flowing when the motors cold. Easy

Find someone with a infared temp reader to check your temp gauge is reading correctly

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.