Greg,

at least in my 1,6TD has been originally two belts.
I had the same problem..only one belt.  Changing from one belt system to two
belt system makes big difference with cooling and charging.  The right
pulley ratios (with two belts) makes pump and alternator round much higher
rpms:

One belt: If motor has 1000 rpms the water pump has 840 and alternator 1595
rpms.

Two belts: If motor has 1000 rpms the water pump has 1400 and alternator
2649 rpms.

The one between alternator and water pump is the nearest to the motor.

Juha Koivisto
88 Vanagon (Caravelle) 1,6TD (old school bus with 9 seats)
TURKU, FINLAND