Could be lack of coolant flow - plugged radiator or perhaps the t-stat.
In some MB circles it's said that pre 1997 104 motors are prone to pre-mature head gasket failure. How old is that item? If weak, the cooling system loses pressure and up goes the temp. There's leaking head gaskets and there's blown head gaskets. The former may not dump oil in the coolant and vice versa, but maybe cause a slight rise in operating temp.
I've always believed the fan clutch was more crucial at slower speeds. Highway driving by it's nature gives a strong flow of air through the a/c condensor/radiator, but it's summer and you now have 2 heat exchangers unloading vs. just the one in winter(radiator), so I suppose it's possible that a weakened viscous fan could play a part in higher temps. Your thread does indicate this parts seems to be doing it's job.