I think we can finally put the cooling system to bed. Here is a
plot of the trip up to GBS.
Once warmed up she sits beautifully in the low 90s for the whole
trip. The dip at the 20 min point is when I flicked on the fan at
the Ancaster traffic lights and left it on right through the village
and the dip at 42 mins was going round the Newark ring road when
there was a fair amount of slow traffic so I put the fan on
again. And the peak at 50 minutes was when I pulled off the A1
through a village and didn't bother putting the fan on. So I now
have a perfectly predictable system.