i think it's closer to 6.9 quarts than 6.6 (read it somewhere here), but i could be wrong.

between mobil 1 synth and castrol syntec, i have no brand loyalties. though last time i went to pick up motor oil for an oil change, walmart was out of mobil 1 - so i picked up castrol syntec.

 

In my experience, I usually end up putting in closer to 6.6 than 6.9, but that's why the engine has a dipstick.

 

6.7 qts. with filter.

Koz

 

My 2 cents is that both are good, and use whichever is more readily available and/or cheaper. Also, are you planning on changing every 5k miles as recommended? If so, you could just use any decent dino oil and save money. A while back a GM engineer was stating in BITOG forum, 'something along the line' that unless the engine is hard on oil (turbo etc.) and require it, there's really no difference in engine wears (between dino and synthetic oil) if you change the oil according to manufacturer recommendation. Maybe, that's the reason why our user manual does not require synthetic. Since it's winter time, you should use 5w20 or if you're a tad adventurous use 0w20.