Consider these things;
If your trips are most often only lengthy enough to bring your engine to
full operating temps or less; then use 10/30 on the other hand if your
trips or daily driving keeps your engine temps at full operatiion levels
just keep using the Mobil 1 15w/50 or 20w/50.
Lower  viscosity oils are necessary if your engine is hard to crank or
seldom gets to full operating temps.
Some care should be exercised when starting a cold engine, those being:
Let it idle for a few minutes before you load your engine, don't race the
engine to make it idle smooth or to get more heat.
There is no doubt that winters are hard on engines but some simple rules
can keep your engine in fine condition throughout these cold periods.
The last word on this is, "unless you're working the engine really hard,
10w/30 should be your winter choice".

Stan Wilder

On Sun, 22 Dec 2002 14:27:39 -0700 Bob Stevens <mtbiker62@HOTMAIL.COM>
writes:
> In my '91 Westy wasserboxer I used Mobil 1 15W/50 all year. In my
> current
> TIICO I also use Mobil 1 15W/50. I'm in Salt Lake City with winter
> temps
> down into the teens and summer up into the hi 90's, low 100's.
>
> Bob
>
> On Sun, 22 Dec 2002, 80 Westy Pokey wrote:
>
>  > Is 20w5 Oil OK in Winter? I drive my van almost exclusively
>  > in the summer and have always used Castrol GTX 20w50 Oil.
>  > Now it is December, temperature is just below freezing, but
>  > the roads in Toronto are free of snow and salt. I was
>  > thinking of using the van to help in my move. I have to
>  > change the oil nyway so I was wondering what weight I should
>  > use in the winter months.
>
> I'd follow the recommendations in the manual.  They won't lead you
> far
> wrong.  It looks like 20W-50 is okay to a bit below freezing.
>
>               _ _
>    __ _ _   _| | |  | David M. Brodbeck (N8SRE)
> Ypsilanti, MI
>   / _` | | | | | |
> +-----------------------------------------------------
> | (_| | |_| | | | @ cyberspace.org
>   \__, |\__,_|_|_| "To the optimist, the glass is half full.  To
> the
>   |___/             pessimist, the glass is half empty.  To the
> engineer,
>                     the glass is twice as big as it needs to be."
>
>
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