BMW: overheating after changing coolant, timing belt tensioner, temp guage

Question
I just bought a '89 325i and the first day I got it I wanted to change the oil and flush the system. After doing so, I started driving down the road and realized that my speedometer was no longer working and that the temperature gauge was in the red.  I changed the thermostat and the car still overheats. I took the thermostat out and car still overheats.  Does this sound like a bad water pump or just one of those problems that I have been reading about with air in the system.  Can you respond quickly if possible.  I just bought a new water pump, but hesistant to put it on cause I feel that I may be wasting my time. Thanks ryan...

Answer
Ryan,
 First I would make sure that the car is actually overheating, and not a faulty gauge.  The temp/fuel gauges on these cars are notorious for malfuncioning.  So if you turn on the key, and the temp guage goes to the red, it's obviously a faulty gauge.  If it jumps to the red after 5 minutes, then you have a coolant issue.  

 I had a water pump fail on my 87 325i this year, luckily I keep an eye on the guage, so I caught it before the temp went to dangerous levels.

 I would definately change the waterpump if you dont know about the car.  They are supposed to be changed at 100k miles along with the timing belt.

 Just on principal, I would change the timing belt and tensioner while I was in there.  You are very close to having the job done, just with changing the water pump, so why not take loose a few more bolts, and do the timing belt at the same time?  Then you will KNOW for a fact that you have a new timing belt, tensioner, and water pump.

 Good Luck,
 Josh