Spent some more time reading up on RAVE. The thermostat starts to open at 85c ±5c
that's a big tolerance! It's fully open at 96c!! Wowser.
RAVE did not say when the viscous coupling does it's thing, just 'at a predetermined temperature' that's really helpful.
So maybe it's ok after all.. hmm will keep an eye on it. RAVE doesn't say anything about the temp at which the AC fans should kick in, does anyone know? I'm guessing the viscous should activate somewhere between 96c (stat fully open) and before the electrics kick in