do you have to purge a supercharger after a water pump change? This is on a 2000 Bonneville SSei

No. You need to bleed the cooling system. The bleeder screw is on the thermostat housing.

I was told that if I didn' bleed thru the supercharger then the motor was toast. I didn't think that the SC had water passages.

No water in the */c. Just use the bleeder screw on top of the thermostat housing like Bill said.

GREAT News. Now I don't feel so stupid. Could you possible know why after changing a waterpump a loud knocking is now heard. Removed SC drive belt and still have the noise. When I get home I'll try to remove the serpintein belt and see if if still knocks. do you have any other troubleshooting tips besides a teardown.

With the belt off and engine not running, does the water pump spin freely when you turn it by hand? I assume your changing the water pump was prompted by a leak, but did anything else happen? For example, did you run the rad low and overheat the engine?

FWIW the SC does have coolant that flows through it to the TB. It does a u turn in the TB and goes back through the SC to the LIM again. However there is no bleeding or worries about either of those two. The only bleeding is at the t stat housing and or radiator cap.

Knocking.. got a vid by chance?

Heres the story. I had to replace a bad idler pulley and belt for the SC drive. After the job I went to wash the car and for a test run. On the way back from the car wash I noticed a knocking sound, and stopped the engine thinking the belt and pulley were coming off. When I noticed the belt and pulley were still good I restarted the motor and saw the water pump pulley had a wiggle and the smell of coolent was there. At that point I drove home and replaced the water pump. When I restarted the motor after the pump swap there was a loud knocking. And that is where I stand. BEEN A NIGHTMARE.

is it a loud hollow knock or a deep loud knock?

Did you overheat it or run it out of water?

These motors take a lot of abuse and well.. it sounds like yours may have a bad bearing.