I am running Redline 5W30 in my Camry and Castrol Syntec Blend 10W30 in the wifes Buick. When I leave for work in the morning it is between -2 and 4 degrees. My Camry fires up on the first revolution. THe starter turns it so fast and easy you would think it is summer. THis is with Redline Synthetic with just under 5000 miles on it. The wifes Buick on the other hand turns over very very slow and fires up with an awful racket! The oil in her car is Castrol Synthetic Blend 10W30 with about 200 miles on it! I decided to check the extra oil I have in the Castrol jug. It is in an uninsulated garage. It was still fluid but also thicker then I thought it should be. I had to shake it very very had to get it to slosh. It was almost as thick as real maple syrup in the refridgerator(sp). This is not meant as a test or as Castrol bashing either. It is meant as a demonstration of how well a well engineered comprimise oil like a synthetic 5W40 can be even when used in the winter! Depending on how the secound oci UOA comes out well be the key factor in how much I like Redline 5W40. SO far I am amazed that a 5W40 can do so well!