I dont think I qualify in the BITOG brilliance dept here but for all it is worth:
An Esso/Exxon bulk rep up here told me he uses XD3 0-30 group 1v POA syn oil in his newer Dodge Cummins diesel all year round because he is a little to cheap to spend a few more cents on 0-40 XD3 syn oil. Few cents compared to losing a $12,000.00 engine, $80.00 per hour repairs + parts?
It can get 105F here and as low as -40F winter. I wont even use 0-40 syn XD3 on my Cummins in heat of summer, I use XD3 15-40 dino HDEO on hot part of summer, and no thinner than 0-40 XD3 syn winter, 10-30 dino would scare me off any time of year.
As far as my diesel goes, I will pay bit more for fuel using a heavier oil than risk damage and repair bills on my engine, that is really expensive at $80.00 per hour + parts IMO.
I respectfully ask why you would risk your engines for a few dollars on fuel savings?
Cyprs