deebo's ek9

ok we replaced the head gasket about 3 months ago i cleand the block up as much as i could because there was so much gunk in the water ways but.
know the car has been runing good no heating up unless im in downtown were the traffic is bumper to bumper but it does not over heat today was the first time the car heated up around my house on my every day rout i opend the radiator and it has antifreez but i spills a lilbit and it still looks like it has some gunk in there does anybody have any idea ????