My radiator over fill keeps emptying out and my temperature needle goes all the way hot when I run my heater, what can be wrong? My car is a 88 dodge aries and I just replaced the thermostat and pressure cap.

Possibly head gasket issue. Also could be radiator hoses collapsing. You sure there is no air in the cooling system?

wow- a Dodge Aries! have the cooling system pressure tested, ASAP, that is a dangerous problem-

Have you replaced the thermostat? One sign that you have a blown head gasket is to smell your exhaust. If it has a sickeningly sweet smell (steaming antifreeze/water) then you need to replace your head gaskets and possibly machine the heads. DO NOT get down and breath in a bunch of carbon monoxide from your tail pipe. Standing a few feet away after the car has warmed up you should be able to detect the odor.