Originally posted by Big Jim:
You should run 5W30 year around. If you live in a very cold area, (Canada, Alaska), you may want a synthetic during the winter.

Along with the other disertation, here is another interesting perspective if you wish to study deeper.

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000427



yeah, and when it gets really cold up here in the winters, we keep the ski-doo primed in case the car wont turn over!!! On really bad days, we all ski-doo to work, you should see the freeways...it's a blast . normally my car starts though as we keep the fire going all night in the igloo...
honestly, it does get cold here in the winters (ottawa is the second coldest capital in the world according to some), but not much colder than many northern parts of the states. Jim is right, synthetic is better in the winters. It also hits 34+ (40+ with the humidex) degrees C regularly here in the summer so I run the synthetic during the summer too for all year protection.