RotellaT blended w/Synthetic OK?

[Locomotiveman]

My Cummins 11 Litre M-11 has 50,000miles. Is there ANY advantage to 'blending' some Rotella Synthetic with the 15W-40 I now use?...Say maybe 20%Syn and 80%mineral oil 15W-40? Locomotiveman

 

[Colt45ws]

I would only do it if the 15W40 is Rotella. If not, it would probably be okay, but thats me being paranoid.
Otherwise it will get you better cold weather performance.