I know it sounds like beating a dead horse once again but I still have doubts on whether to switch from 10W30 to 5W30 grade during winter. I live about 1/ hour from Ottawa, Canada in a remote (read rural) area. Temps over here can easily get down to -40C (that's exactly -40F!).

I have debated the issue with my dealer and from his point of view, there is no need to go with a lighter grade since 10w30 covers our temp swings all year-round and it's synthetic to boot, hence better cold mornings startups and very little degradation. He mentioned that 5w30 can cause some valve stem noise in the long run with using lighter oil...

Here's an excerpt taken from a web site doing oil comparisons:

Viscosity Flash Pour %ash %zinc

10W30

Mobil 1 160 450 -65 --- ---

5W30

Mobil 1 165 445 -65 --- ---

Notice the little difference in viscosity and flash point. And the pour points have identical numbers. So what's the point then in selling 5w30 when 10w30 does all we need. I may also be wrong in stating that.. Please shed some light and share your experiences.

Thanks!