Ford Repair: 1995 Ford Escort Overheating, radiator cap, water mixture

Question
My 1995 Ford Escort overheats when driven in the city, but when on the freeway, it doesn't seem to have the problem.  What happens is I will be driving and I can hear it boiling in the radiator.  Then, when I stop, it boils out onto the ground.  I haven't checked anything on it, but I just wanted to find out what the most common reasons for this happening are.  Thanks.

Answer
when you say drive in the city is it stop and go-and a lot of idling if so you may have a cooling fan problem-not coming on during these times-it would not come into play during highway driving because airflow thru radiator would be sufficient without the fan at those speeds-

other things could be dirty coolant
coolant fan switch

thermostat is not likely since it has no idea whether you are in city or on highway but i would replace it when the problem is found

check your fans close-and make sure your radiator cap is good (rubber seal not tore or broken) and coolant is at least 50/50 with water mixture
good luck.