Not an aux fan issue if your temps while driving are too high. Aux fans have no effect above about 20 KPH. Others can advise you better about radiator replacement, but it does seem that the temp differential between upper and lower rad hoses should be more than 4-5 degrees. I've always been told it should be in the range of 15-20 degrees. Maybe a radiator expert will weigh in.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't