There is no gauge. You will get a warning if the temp gets too high. I thought that was weird too when I got my 335 because my last bmw had the temp gauge, and now I have an oil temp gauge.
Anyway you can still access the temp through the hidden onboard computer menu:
Here is a site which lists all of the hidden menu codes:
http://e90.wetpaint.com/page/BC+hidd...us/revision/37