Sitting in heavy traffic on the M56 into Manchester today, no worse than on the M25 but today the weather was truly HOT. This seems to have made the difference as the coolant temperature went up to ~120 degrees which is a bit on the warm side. It cooled down towards 110 when the traffic started moving but clearly the new radiator & original Spal fan (385mm) are struggling to cope in standing traffic on a hot day.
Options under consideration are changing the fan (from a single to two [smaller] ones). removing the blanking plates on the rear ‘kidney’ shape bonnet vents and/or… drilling some holes on the rear face of the bonnet where the engine bulge drops down towards the bulkhead. The latter is a bit drastic but a possibility if the other options don’t do the trick.