loosing coolant randomly on 1999 Dodge Grand Caravan

I have a 1999 dodge grand caravan,3.3 liter, and so does a buddy of mine. both of them loose alot of coolant in city driving conditions,on the highway they dont seem loose any,it seems to be coming from around the radiator cap that is the only place i find evidence of water leakage,so i replaced the radiator cap and it improved but it still does it,i thought maybe the overflow tank line may be plugged but its clear,I cant find leaking anywhere else.ALSO IT IS NOT OVERHEATING OR HAVING A TEMPATURE RISE AT ALL even driving up a mountian

Does anyone know of this problem

Asked by for the 1999 Dodge Grand Caravan