Some block heaters heat the oil dierectly but most heat the coolant and therefore passively heat the oil.

I think the coolant block heaters can get to well over 140 degrees, depending on conditions and size. Some come with switches to keep the temp from getting too hot.

Apparently the drain plug idea is a no go because most heaters are too large and hence use the freeze plug area. I've found some magnetic type heaters and also some lower heater hose types. The lower hose type seems the most feasible.

I used to use a magnetic type oil sump heater on my old Honda. My drive to work is less than ten minutes and the temps will drop down into the teens and twenties here in the winter. Prior to driving off I could pull the dipstick and feel that the oil was indeed warmed up. It was worth it for such a short drive.

Where would you put it on the M3, seems like there isnt a lot of free space...

Just for reference sake, here is the heater I picked up for the 318:

http://forums.pelicanparts.com/uploa...1098408750.jpg http://forums.pelicanparts.com/uploa...1098408773.jpg
And this is the instruction sheet that came with it. The numbers seem to have been updated though:
http://forums.pelicanparts.com/uploa...1098408868.jpg

There is no thermostat on this heater, so depending on the ambient temp, the engine can get warm enough to use the interior heater nearly immediately. I'm not sure about the rad/heater hose types.

Tim