My Aux fan should pull, correct? I think I may have found the problem....

 

YES

 

Hi all,
With thanks to everyone. The problems were twofold
- polarity incorrectly reversed causing the aux fan (which is a modern replacement unit) to PUSH rather than PULL hence disrupting radiator air flow
- a defectively overfirm/failing viscous coupling prematurely and excessively firming up leading to loud roaring and excessive air flow

Now it was 30 degrees C ambient yesterday and my viscous coupling gently cycled on and off depending on road speed and thermostat state as one would expect, and my AC is icy cold. Mystery solved!

 

Well done!

 

Yep, well sorted and rectified.

Again, "Simple cars these V12's"