I've posted here before about htis problem and got some very useful comments
particularly from John. Many thanks.
Tried to do some extensive testing on W124 E220 1995 which runs an
equilibrium of about 92 idling rather than an optimal 80.
I've just run it for about an hour. I noticed that although the main water
pipes leading into and out of the radiator from the engine block were very
hot the looped tubes poking out down each side of the radiator (2 columns of
8 double loop-back pipes that presumeably take the water horizontally
backward and forwards across the radiator) were not hot at all.
Is this definitive proof that the problem is a blocked radiator?