Find a new mechanic.  I have had the same problem. Took over
a year to find the exact reason, (a vacuum hose off). In the mean time
there is a chemical test you can use to tell if there is any leak
from the head gaskets that would cause  over heating. For back
pressure in the exhaust remove the O2 sensor and run the motor with
a pressure gauge in place. The gauge should not read more then 3 LB.'s.
Assuming the cooling system is working propperly a lean mixture in the
fuel system could also cause overheating.

            Eric                   86-VW4x4
            vw4x4@fyi.net          72-240z
            Pittsburgh, PA USA     1936-Chrysler

On Sat, 1 Aug 1998, Curtis Gatlin wrote:

> I have been overheating lately.  My mechanic says there is back pressure in my
> system.  I have an 86 synchro with 196K, no history known on vehicle.  My
> mechanic says I should replace the head(s), however there is no guarantee the
> bottom end will hold up, the charge for the heads plus install is $1600 for
> both sides, using new heads.  Complete rebuild using all new German parts is
> $3200.  Is this too much.
>
> Curtis
>