oil for -30f winters

[gfl@cc.bellcore.com (grant f lenahan)]

Tim:

For *real* cold (-30 qualifies), you need a 10-30 or 5-30
dino oil.

Well actually, you would really benefit from a
synthetic - good flowability with good film strength
at higher temps - just what you ordered.

Now, you say you don;t want synthetic due to your 2.5k
change interval.  Will you breach a contract if you
change your oil every 5k with synthetic?  Why is
this figure so critical, if other factors outweigh it?

Grant