I have a 1991 300E that the temperature gauge rises up to the 120 degree mark when sitting in traffic. When moving temperature reading is at 87 degrees and on occasion may rise to 100 degrees. But if I get stuck in traffic on a hot day the temperature rises up to 120 degree mark. The car has not physically overheated as yet. I'm beginning to think the auxillary fans are not coming on. Is there a procedure to check the to determine if they are the problem??? Any help is appreciated.

Thanks
Chris