Temperature Switch

I have a 93, 3.0L engine. During normal operation, the engine temperature is just below the middle of the dial (in the dash). If I do lot's of idling, stop and go, the temperature will move just above the middle of the scale. After that, the fan will kick in and out.
I have two questions. At what temperature should the fan start? To me it should not start until the engine is getting hot (not just above normal temp). Do I need a new switch?

When the fan starts, the entire car starts to vibrate. It's like the fan is not balanced or the bearings are gone or the engine doe not compensate for the extra load. It there a lube point for the fan? Can I lube anything.

Thanks for the help