My 1995 E420 was running hot - not quite as hot as your, but close. it has essentially the same engine. I was able to attach a resistor to my coolant temperature sensor - now my car thinks that the coolant is warmer than it actually is - and activates the electric fans to keep the engine cool.

I first replaced my electric fan power resistor (it allows for low speed fan operation by running some of the current through a power resistor). I'm not sure if the 1997 has the power resistor like the W124 has. Perhaps a W210 E420 owner could chime in and help.

So - check for the power resistor (it might be bad), then check to see if your model allows for adjustment of the coolant temp. sensor's resistance.

Regards,
Troy K.
1995 E420
83k