Thanks Arthur. Actually it doesn't come down when the auxiliary fans kick in. It stays low, around 80C (remember, thermostat removed)when on the highway. When I'm stopped in traffic it immediately starts to rise. The aux fans kick in at some point, but the temp doesn't drop back down. If I put the car in neutral and rev the engine to 1500-2000 rpm, the temp then starts to drops.

Ken Fuller
1990 300E
145K miles