Well, i will repeat myself but it's a pleasure.

From VW America: The normal temp gauge position should be just over the
light (coolant level light), the fan should kick in a t about 3/4. For an
2.1L engine, that is with the new 87deg thermostat and the new engine
temperature sender (the black one in front of the thermostat housing).
True! I have both, the old and new one (thermo. and sender) (or should I
say I had, sniff).

On my van:
Position of needle whit old temp sender and thermostat:
Normal driving: Needle just below light
Traffic: Needle just over light, fan kick in and hold temperature just over
the light or on the light.

Position of needle whit new temp sender and thermostat:
Normal driving: Needle just over the light.
Traffic: Needle 3/4 (or a bit more), fan kick in at 3/4.

This proves that the new temp sender (temp gauge) is giving a higher
reading, about 20%. It doesn't mean that the engine run's hotter.
The new thermostat also open a bit later than the old one, this will keep
the engine running a bit hotter.

The thermo switch as nothing to do with the thermostat or the temp sender,
it's just a switch that goes ON when the rad is too hot.

If you had a defective thermostat (in the close position), the engine would
be very hot and the front rad cold!!!. So the thermo switch would never
open because the rad would be cold.

The bleeding of the 2.1L is a lot more easier than I was expecting, if you
look my site you will see that I did too much for nothing. 10 days ago we
change the coolant of and 88GL, we didn't even raise the front, but the
driveway had a good inclination.

If the coolant system is clean and working properly, the rear section
(mostly the engine section) should auto-bleed in a matter of a few miles
(10-40). The front section (radiator) will not bleed itself; you need to
force the coolant (revving the engine at 2000rpm) to this one.

Changing or servicing the coolant: No need to get all the old coolant out,
if you open the screw under the engine heads you should get about half of
the old coolant out, that is enough to regenerate the coolant propriety for
another 2 years. If you want to get some more, simply disconnect one of the
2 main line (big tube) under the van, you will get another 1/4.

See by bleeding section at:
http://www3.sympatico.ca/huotx/bleeding.htm
http://www3.sympatico.ca/huotx/front_radiator.htm

Cheers and good luck, Ben
http://www3.sympatico.ca/huotx/engine1.htm