I have a 97 E320 with the same engine.

I wonder how fast your coolant temp comes up to the 87 deg C area. After a couple miles?

If it takes a long time for the coolant to compe up to that area or never reach that area, you might have a fatigued thermostat (common failure) that cannot close completely. All the MB stats that I have replaced (three of them) all failed in that mode and they typically last about 60kmi.