I have 4 qts of Chevron Supreme and 3 qts of Exxon Superflo, both 10w-30, both API Service SM.
Is it OK to use these two oils together in my Ford V-10 engine?
Yes, if that’s the grade called for by Ford.
Yup–as long as the engine calls for 10w-30 oil, then you can feel free to mix them.
It seems to me that there is a government standard that oils of the same viscosity and API service rating have to be compatible. In fact, even oils of different visosity and/or API service ratings are probably compatible. When I have rented U-Haul trucks, I’ve been told that if I check the oil and its low to put in a quart and I would be reimbursed. I was never told what kind of oil to put.
Standard Oil is Standard Oil…