Originally Posted By: CATERHAM
If mixing two or more 0W oils, or 5W oils together or even 10W oils for that matter of any brand resulted in the loss of an oils cold viscosity rating category certainly ASTM D6922 or ILSAC GF-5 would deal with it. It's obviously not an issue despite you're efforts create one.
STLE paper on cold temperature performance of lubricants.
Demonstrates that different PPDs have different effects depending on which VII and basestock is used.
Making a mix, which in all likelihood unless the same brew from the same manufacturer means that
a) there are now 4 VII/PPD interaction/compatibility issues, two of which were resolved by the oil manufacturers (possibility is that they found one of the interactions not beneficial)...thus my statement that sticking to (say) M1, Redline, is less likely to not end up with the W that you think.
b) each of the additives is potentially halved in concentration, and you have blind faith that two halves is as good as each whole, which is not necessarily the case...thus my statement that sticking to a manufacturer is more likely to get the anticipated results, as they are more likely using the same products, so you will be using closer to the original concentrations, not two halves.
I'm certainly rethinking my mixing, but at -11C the worst possible conditions that my vehicles will ever face, I don't think any VII/PPD is going to stop the oil flowing.