the 6.9 will hold 10 quarts easy, and 11 with the PSD filter on it.

As for oil, in my truck and my stepfathers PSD all we ever have run in it is Delo 400, mainly cause we can get it in a 6 gallon case at costco. So he gets his 15 quarts and I get the rest

IMHO additives in oil aren't the best idea, my reasoning for this is that the oil is designed to lubricate and help cool the engine down. And by adding in say a quart of oil additive there's one less quart of oil that you have I'm the motor to help cool and lubricate it.

 

Form what i heard adding lucas oil additive is a smart choice.

 

I've run the delo and the Rotella,they are both good stuff IMO.

 

Always have ran Rotella myself