Does oil weight in the winter make any difference once engine is at operating temp?

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324
I've been confused for years about using lower viscosity oils in the winter. Is the lower "w" winter number the only thing that counts? My truck using a 22RE engine is usually preferred to run higher viscosity oils once at operating temp (up to 15w-50 in some cases). Unless the air is so cold the engine never gets to full operating temp, shouldn't the second number not matter at all in terms of the season? I should go with a 5w-40 in the winter instead of 5w30? Summer is a 10w-40 oil. It doesn't get cold enough here to prevent an engine from reaching operating temp, and if it did, I would just block the radiator with cardboard.

With modern synthetics, is the lower W number the only thing that counts for winter? Back in the day, one would be using a conventional oil that can't span such a wide range of viscosity attributes and you had no choice but to lower the operating temp viscosity in order to have something that was better flowing on really cold starts.
 
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example a 0W20 will flow better during cold startup and winters then a 5w20. at operating temp they would perform the same. only diff is the cold temp viscosity. 0w would be thinner then 5w which would be thinner then 10w
 

MrPlow

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324
example a 0W20 will flow better during cold startup and winters then a 5w20. at operating temp they would perform the same. only diff is the cold temp viscosity. 0w would be thinner then 5w which would be thinner then 10w
So it makes the most sense to keep using 40 weight all year long and just switch to 0w or 5w depending on season? Highest grade synthetic of course.
 
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