NEED HELP OVERHEATING PROBLEM
 

I have a 86 gt i can drive it for a good 30 mins before it starts heating up and its doesnt matter if im in traffic or on the highway. we have put a new water pump,radiator cap,thermostat and the fan and radiator is fine. we can a check for a head gasket leak and it checked out fine but im still thinking its a slow head gasket leak dont know what else it could be. any input would be much appreciated

Make sure that your system is working correctly. For example, when the car warms up, feel the upper hose to see if it's hot. If it isn't, your t-stat is sticking. Feel also the lower radiator hose. If it's the same temp as the upper hose, your radiator isn't cooling down the coolant. Is your pressure cap good too? Any leaks (besides head gasket) or air pockets in the system? Also, does it over heat at idle too or just while driving? If just when driving, check the air flow to and through the radiator. Also, on the topic of head gaskets, are they facing the correct way?