As you can see from this:
http://www.tdiclub.com/TDIFAQ/TDiFAQ-10.html , CT diesel should be good to -17C (about 1.4F). If you feel the need to go lower, there are many options.
You should also read the recent thread about anti-icing additives:
http://www.e90post.com/forums/showthread.php?t=786433