Hi, will removing the water pump drain bolt (20mm), drain all of the water out of the engine?
Will the radiator drain also?

Cheers Ian.

 

I'm answering my own question for anyone else who needs to know.

The A6 1.8T 1999 auto estate takes just short of five liters of coolant, removal of the water pump drain bolt will remove all but 200ml which will be in the bottom of the radiator.