Should I be concerned almost overheating.

I was driving home in stop and go traffic today with the air blasting 120 degree weather today here in scottsdale az when all of a sudden i feel warm air coming out of my air vents.

I look down and the temperature gauge is one notch away from the red. I roll down my windows and turn the heater on full blast. This was absolutely miserable.

The temp came down really fast and i drove the rest of the way home and the car has been sitting outside since. Opened the hood coolant is to the max line.

Should I be concerned or could it just be from a really hot day and stop and go traffic going through downtown scottsdale?

Just got all the mounts done a couple days ago hopping its not something else again.

/\Ditto/\

Another culprit on temp gauge is a bad temp sensor at back of head. However it normally just reads wrong numbers. It usually does not cut the A/C compressor. Like QTD said, normally it is the fan or T-Stat. Fan is easy to check and T-stat not a bad thing to change if it has not been changed in a while. Also ONLY use the VW T-stat or else you will be doing it again soon.

I had an overheat situation that was caused by the original thermostat stuck closed. You should verify that the thermostat is opening at the correct temperature with a pot boil test.

Checked the electric fan and the connector down by the lower rad hose they were both fine. Turned out to be the thermostat. Thanks for the help

Exact same scenario here. The wife reported that the AC would run for a while and then the compressor would disengage after the car had been driven a while. I had previously (years ago) experienced the same issue with the 384 relay, which I took out resoldered and it fixed the problem. Therefore, I replaced the relay expecting it was the same problem, also noticed the coolant was low and topped it off.

Then when I drove the car, I noticed it was overheating (going up to almost red line), whereas it had always stayed rock solid on the 190 mark in the past. This over temp situation is what caused the AC to cut out (just what you want in 110 degree AZ heat).
I checked to make sure the electric fan was working (it was) then suspected the viscous fan coupling - but after research here, I ruled that as highly unlikely. Since I was losing some coolant, the head gasket seemed a possibility, but I was hoping for something simpler. Decided on replacing the thermostat and that completely solved the problem. These instructions are good:
http://www.myturbodiesel.com/wiki/thermostat-removal-and-replacement-b5-passat-tdi/

For $15 and less down time, I just bought a new thermostat and didn't bother testing the old one. I also bought a new thermostat housing, but didn't end up using it. Didn't even detach the old one from the radiator hose. Drained the coolant, removed the two bolts (a little tricky), put in the new thermostat and O-ring and reassembled. Cheap and easy. No more overheating and no AC issues.

FWIW, I would highly recommend getting the VW t-stat. I have had several issues where people install an aftermarket unit and within a few months have issues with it opening too early or not at all. AZ heat is no place to take a chance.

The VW unit is like $35-$40