Follow-Up:
This happens due to engine misfires and usually accompanied by the "Check Engine" light coming on steady. If you haven't ever had it done, you may want to get the fuel injectors cleaned (or even just use an off-the-shelf fuel additive for a couple of tanks) and change out the spark plugs. This might help with the misfires and stop the problem at the source. My temperature gauge does the same thing, never gets about 190. I even have the equivilent of a VAG-1551 diagnostics tool and when I hook it up and have it check via the various sensors, it also returns a similar figure. Just out of curiosity, why will a cat burn-out not be covered the third time around? It's my understanding that the catalytic converter has an 8 year, 80k mile warranty on it, and you can usually get them to repair it for free even beyond that since it has to do with controversial emissions issues.
Here is a link that might be useful: MotorHomepage Rialta Resource