A few weeks ago our cars temp gauge starting rising only when we were stopped fairly quick. When we drove, it would gradually go down to normal. Our heat also only works when we drive (Foot has to be on the gas continuously). I suggested changing the radiator cap or tightening it. WE tightened the cap and it worked car went back to normal. We bought a new cap thinking the other one was bad and the car went right back to doing the same thing it was doing prior to anything so we put the old one back on and it quit yet again.. WE obviously know something is wrong but figured we had a small window to get by to get money to have it looked at. Recently the temp gauge has been going up to dangerous hot levels within a few minutes of starting the car. I never see any smoking, hear any bubbling even the car will still have frost on the hood.
Is the car really over heating? Can someone give me some advice on what could be causing this or what else to rule in or out, so I don't get jipped by a mechanic for money and I can go strait to the source, thanks.