Engine Coolant Temperature Gauge question

[Snoopy]

syljay wrote:

> [ ][][]  |  [ ]  |  |  [ ]  |
> . .                  . .
>   C                            H
>   1 2 3   4   5   6  7   8   9

> Question 3:
> I think the dots for positions 1 and 7 are calibration test marks. If 
> I remember correctly, the Bentley shows usage of a "Special Tool" to 
> test the gauge. More than likely the tool is just a rheostat. Does 
> anyone know the resistance values at the two test positions?

The 'special tool' is indeed a simple VW 1301 rheostat. This link shows 
dependence between its values and real ohms:
http://www.bentleypublishers.com/tech/vw/bentley.vw1301.testing.htm

Now Alldata diagnostic says first to disconnect the temperature sensor. Then 
ground the terminal T of the connector 
(http://www.sjmautotechnik.com/trouble_shooting/ecupic/mfts_conn.jpg) using 
the 'tool' set up for 660 (you can calculate approximate ohms using Bentley 
table, plot a graph or use Excel). Turn on the ignition, the gauge should stay 
between first two dots. Then, adjust the 'tool' to 50 (34 ohms), and the gauge 
should stay between another two dots (hot position). I've successfully used 
simple resistors to simulate these two positions, worked fine.