I wonder how Amsoil 20W50 would do in the sub-zero temperatures? Being a
full synthetic, I would assume better than conventional oil.  The below
study (probably sponsored by Amsoil) makes a strong case for using the
product.  Interesting read either-way.

http://www.synthetic-motor-oil-change-and-filters.com/amsoil_articles/oil-co
mparison-on-the-dynometer/

I have a 91 Westy with 56k original miles, just purchased by my friends,
sitting in my driveway and we haven't been able to get it started since the
temps dropped below 10 degrees.  It will only crank for a few seconds,
cough, tries to turn over, then nothing.  Checked the battery and there is
just under 600 CCA left on it, cleaned the terminal posts, even tried
jumping it for a bit more power.  Nothing...  There is no rush to get it
going, except the blocked driveway, and I am not about to crawl under it at
-4 degrees!  I will probably wait until it warms up, probably by July!!

I think the oil is just too thick, not sure what is in it.

Jack