My 1992 Buick Riviera with two speed electric radiator cooling fans runs hot in traffic. The temp guage normally reads mid range until I get stuck in traffic with the air conditioner running.
The two radiator cooling fans fail to switch into the high speed output mode at the appropriate time causing the temperature to approach the 3/4 mark. Occassionally the fans will kick into high gear but not always. I replaced the switching relay without success. I suspect I have a defective sensing unit that controls the fans but not sure where and which sensor that might be.