Nothing wrong with running 5W-30 in the colder months. Makes good common sense depending on where you live. I can see that if you live up North for best fuel economy and cold starting. 10W-30 will cover you to at least zero degrees F or -18 degrees C and if the temperature stays above 60 degrees F. 5W-30 if the temps never get above 60 degrees F. Important part is not to use multi-viscosity oils outside of this weight recommendation or 20W-50. Also, nothing wrong with running synthetic motor oil especially if the temps drop below -20 degrees or all around use. Glad I don't have to worry about it.
