Overheating problem

[VWNobby@aol.com]

I own a 97 Jetta GLX with 56,000 miles on it. About 3 months ago or so I 
noticed that the temperature gauge (coolant temp.) started to go past the 
center marker. At first it would only go a few degrees past the center mark. 
But lately it actually reaches up to 230 which is 3/4 of the way through. 
Usually I open the vents and have the heater on full blast to cool it down to 
the center point. But obviously that's a temporary fix. Today I noticed that 
the gauge reached about 220 then dropped to the center and then eventually 
went past 225, all within a 30 minute drive. Even at highway speed I have 
this problem. I have checked the coolant level and it is fine. Both the fans 
are constantly working, so I am pretty sure that isn't the problem. I 
installed a G-Chip about 3 months ago and I am wondering if that may be part 
of the problem (I would think that since there is more power coming from the 
engine it would tend to run hotter). Other possibilities that crossed my mind 
were the thermostat or the coolant pump, but how can I pin point the trouble 
spot. If anyone has run into a similar problem, please let me know. Any help 
would be greatly appreciated, I'm sure this problem can only be detrimental 
to the life of my car. Thanks in advance.

Norberto Luis
97 Jetta GLX
Black