Thank you (obvious really.....Apologies for such a bone question)
This explains a few things
My 1.6 runs cooler as the FAN spins quicker at 2200 so is louder than my 2 x 1.5 that run 3c hotter where the fans never go above 1800 so they are noticeably quieter.
All 3 have pull fans on the "open end" in preparation for the English summer