I've just started to drive my car to work regularly. its about a 25 min drive on every type of road. I'm having some issues with the voltage dropping down after about 10-15 mins of driving and throwing my guages off. temp, press, gas. with less volts my temp goes up and my gas guage goes up and my oil press goes down. anyways, my heat goes way up and i put the heater on full blast to make keep it in check. it only goes up when my volts go down, but I figured I turn the heater off the temp will be high but if it doesnt rise its just the guages. thing is, it does rise. and its weird. the temp is low in traffic but high on the highway, the opposite of almost every other car. its a 350sbc with a couple smal mods done, cam, intake, carb, exhaust. i'm using a stock rad and an electric fan from an '87. the coolant is full, anyone have any explanation? seems to get hotter as it stays in higher rpms.

 

Do you have the air dam under the car? Usually, overheating on the highway but not at idle indicates that the air dam under the car is missing.

 

Yup, I've got the dam on. its not necessarily on the highway, but whenever i'm at rpms above 1600 for a length of time. and the water pump is brand new. so are the belts. and tstat.