Originally Posted By: nepadriver
Originally Posted By: CATERHAM
Originally Posted By: Maxima97
You can mix a Qt of M1 0W20 with the 0W40 to make it thinner. But unless you intend to do 10K OCI, using such good synthetic oil mix is a waste.
I don't know why you would describe your suggested blend as a "waste". It's actually a good idea is you want to make a higher VI 0W-30 than what you can buy although you'll have to use a lot more than just one quart of M1 0W-20, more like 60%.
Is there a thread that breaks down that mix ratio you could link to?
Also, in a towing scenario wouldn't the 0w40 be fine, or very hot climate, or both, if the owners manual specifies it as such?
Using a viscosity calculator like Widman's will allow you to determine the percentages of each oil to get the desired final viscosity:
http://widman.biz/English/Calculators/Mixtures.html
Yes using a 0W-40 would be of course fine if the owners manual suggests it but GM doesn't. The specified 5W-30 grade or equivalent 0W-30 with the same HTHSV has more than enough viscosity reserve to deal with the resultant higher oil temp's that may result from some extreme usage like towing in the mountains on a hot summer day.
Also oil shear and possible fuel dilution are also factored into the 30 grade oil recommendation.
Put another way, for more typical none extreme use you could very likely use a 0W-20 oil grade which many OEM's are specifying today including GM.
If one is really concerned about their oil choice not being up to the task simply choose a synthetic oil of the specified grade which will handle high oil temp's better than an off brand dino.