86 560 SEL Close to overheating?

I've replaced both the radiator and the fan clutch. Temp stays below the 100 degree mark(line above the 80) regardless of traffic or A/C being on. After driving for about 45 minutes, temp will rise to about 110, regardless of speed of vehicle. Temp does not drop even on highway. If car is shut off, for lets say a half an hour, then the same sequence begins again as described above. Thermostat was replaced over a year ago. Aux fan is coming on but has no effect. Any ideas? Could T-stat be bad? All other components have been replaced in the past month. Prior to replacing radiator, temp would approach the red mark in traffic without the A/C on! Now it is much improved, but the above happens.