overheating?

I have a 1994 sl2 5spd dohc. Lately i have noticed that when i drive in traffic or even at an idol my temp gauge redlines and the fan turns on. What is making my car heat up so quick? For example, i can be at a drive thru line for 3 minutes and the gauge is already reading the redline. I have plenty of coolant and i just replaced my radiator....no more leaks!

you may have a bad ECT or thermostat, maybe old coolent or something jammed up near the radiator. but chances are, nothing is wrong, i know the S-series temp gauge reads a little weird compared to other cars. but keep in mind when you are moving, the air moves heat out of the engine compartment. when the car isn't moving, the heat just sits there, acuumlating. it been a while since i drove my S-series, but i do remember a few times the fan kicked on as i was leaving a drive-thru. anyone else have opitions?