'86 5000 CSTQ Overheating...

[Todd Joseph <todd@ConnActivity.ConnActivity.com>]

I'm at a loss for the cause.  I replaced the heater core about 3
months ago.  The car is not losing coolant. I put in Prestone
Antifreeze.  I normally drive the car 2 miles or so in the AM and 2
miles or so in the PM (back and forth to train).  Today I drove it 25
miles into Boston and 25 miles back.  The car ran fine for the first
20 mins each way, but then Temp light came on and the car ran at rough
idle at low speeds.  On the way home, the car actually stalled once.

I called the local Audi dealership and they mentioned that I should
have used Audi certified Antifreeze.  Is there any truth to this?
Barring this being a simple problem, can someone recommend a good
mechanic in the Boston Area?  The car has 200K+ miles on it.  I don't
want to pour much $$$ into it...

Thanks for any help!

Todd
todd@mail.connact.com