My wifes car, 84' 300dt with around 200,000 miles, has just started (yesterday) to overheat badly at idle. When driving on highway the temp is around 85C - 90C with AC on, this is summer in florida so its hot out. When she stops in traffic or drive through the temp jumps to 120C quickly. I haven't looked under the hood yet but does this sound like a problem with the Aux cooling fan not kicking in? And if so, is this an easy fix.

Any help much appreciated

Thanks