Overheating problem?

["therealdmcvegas" <DMCVegas@xxxx>]

I'm currently having a new problem with my car overheating, but not really. Let 
me explain...

The temp needle will move as normal, but will not go past 220 degrees. 
Today for example, I was driving home with the A/C on. Cold air was blowing, 
and the needle was staying right on the 1st white line. Yet I seems to still have 
the coolant bottle slowly boiling over. I say slowly, because it isn't the same as 
when I've lost the alternator belt. When that's happened, steam has blow up, 
and out of the engine cover. In this case, coolant has been dripping out of the 
hose, and has been foaming up around the radiator cap.

Another odd thing was this. I went to lunch today, and the drip occured. When 
I left work about 4 hours later, the motor was cool to the touch. But, when I 
opened the overflow tank, the pressure inside of the system was pretty strong. 
It took about 2 seconds or so to stop the hissing, and the coolant inside had 
air bubbling up thru it.

Now I know that I should perform a pressure test on the system as a general 
rule, although the system seemed to keep the pressure up pretty well on it's 
own. But I do have a couple of questions/concerns as to what the problem 
here could be:

1. Defective Radiator Cap.
2. Sytem has too much fluid inside preventing expansion (I did top the system 
off last week, although it was because this problem occured first).
3. Possible Head Gasket leak allowing exhaust gasses into the system 
allowing it to be pressurized?

I also though about a possible sticking thermostat, but since the temp was 
stable, I figured I could rule that out.

Any input on this subject would be greatly appriciated. To give out a little back 
ground info, the water pump is over 2 years old, and the radiator cap is almost 
2. I also have the stainless bottle, and the overheat protector.

Thanks in advance!

-Robert
vin 6585 "X"