One thing i forgot to mention...

the stage 1 and stage 2 temp specs on the thermoswitch that
activates the radiator cooling fan were lowered in the 85-86 year
change when the 1.9L was replaced with the 2.1L. the later model
switch activates stage 1 at a lower initial temp and stage 2 (high
speed) comes on at the temp that stage 1(low speed) did on the early model
switch.  does this tells us that VW saw a problem with overheating
and made a production change?

the 2.1L doesn't seem to get quite as hot at idle as the 1.9L did, so 
maybe this lower activating thermoswitch would help current 1.9L 
engines too.  It's about $35 when i checked into changing it on the 
1.9L

-dan