I agree. 5-40 Syn made a cold starts smoother for me. With my new GP's I can start down to about 10F without a block heater (I hate Chicago street parking!).
Just remember that the lowest temp overnight is what your block is going to be close to several hours into the day.
Take your battery inside, charge it if you can, and give it go later in the day. Good luck.

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1987 300SDL-268k mi