Cold Weather Motor Oil Recommendation
Apologies for diverting off of the OP's original question, but I believe this is cogent to his apparent desire to find ways to improve cold weather operation of his vehicle. This is almost pure opinion, so please take it for what it's worth, especially considering it is free advice.
While I recommend and use block heaters in my vehicles, I personally believe that choice of motor oil is most critical for cold weather operation. This is especially true when you consider that you won't always be able to plug in your heater in all the locations you may park.
The LO9-2320-289-12 Lubricating Order Technical Manual specifies 10 weight viscosity oil for temps between +40 to -25 degrees F (+4 to -32 C).
Of course, this is from 1992 when synthetics were less well understood and affordable.
Warning: Motor Oil Opinion Alert! (recognizing that people can be very passionate in their choice of lubricants)
I have been running Rotella Fully Synthetic T6 in all of my diesels for years and have had great luck with it. It is a 5W-40 viscosity oil that I run year round. While there may be technically "better" oils (Amsoil comes to mind). I find that the T6 provides the best compromise between cost and performance for my needs. And do my trucks start nicely in the cold!
Some of Shell's marketing:
http://youtu.be/MEaf5ES6Xmg
http://www.shell.com/rotella/products/t6.html