I have this question posted in the 3Series E46 section also.

I am getting ready to change the coolant in my '00 328. I've read a lot of DIY threads that have been posted. They all seem to state that the block drain screw is a regular type bolt, 13mm I think I read.
All I can see is a hex or allen type screw that appears to be a 6mm. It is right where the exhaust comes down.
Could this be the block drain?

A '00 328 would have an M52 engine and the block drain will be on the lower part of the block on the exhaust side roughly between cylinders 4 &5. Memory says that it is a flanged bolt type plug and a 13mm head sounds about right.

Okay, I just got done doing coolant, thermo, w/p, and belts.
The block drain was indeed a 6mm hex bolt. Strange. Different from what I've read.
Both belt tensioners were T50. Also different from what I've read.