Passat 2000 V6 engine overheating
 

Hi,
I have a 2000 passat V6 manual transmission. I have started experiencing an engine overheating problem. After driving for about 5 mins today, the temperature shot to 250 and the 'stop engine' light and alarm came on. From that time onwards I had to start and stop many times until I reached home as the 'stop' and 'check coolant' alarms kept coming soon after I started. The coolant was almost boiling, but the coolant and engine oil levels are fine. I have changed the timing belt, water pump and the thermostat a few months back at 85,000 miles. The car has 90,000 miles on it now. An additional information - just before this problem occured, the A/C didnot start for a couple of times, although later it was working fine.
Any suggestions as to what might be the problem...