change thermostat

[MercedesMike]

For the 617 engine, you want to plumb parallel.

When the climate control is off, it's valve that regulates coolant flow (called the Monovalve) is closed. Therefore, all your coolant flows through the WVO system. Im assuming you are not blasting the heat most of the year, so this is perfectly fine.

However, as long as the coolant return is T'ed in somewhere between the monovalve and the stock aux pump, the stock aux pump will pull water through both circuits.

Ive never heard of a mercedes WVO conversion of any variety with 2 aux pumps. You definitely dont want to introduce more modifications if you can help it - you are already adding enough.