'16 Buick w/ 3.6L: 5 qts. or 6?

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Today I had the Buick's December oil change done, with Castrol Magnatec 5W-30 dexos1 oil and a Mobil 1 filter. The owner's manual says it takes 6 quarts, so I brought an extra quart of SuperTech. However, my regular mechanic says the car was reading full on the stick after he loaded the 5 quarts in. I drove home, waited about 10 minutes, made sure the car was level, and checked the oil myself. The new oil, though hard to see, is clearly between the Add and Full marks.

What gives? Perhaps some of the old oil is still in there. If you have a 3.6L, the later engine (2013? to 2016), how many quarts does it actually take?
 

Benzadmiral

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Should be 6 quarts. Has the dipstick been changed at some point?
Not on my watch, which has been some 16 months. However, I see that on the July '20 oil change, he put in 6 quarts, and the car certainly never read overfilled when I checked it. Could most of a quart of old oil just not have drained?
 
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I’ve seen the dipstick readings vary after an oil change, when using the “same amount “ of oil. It makes me wonder if some companies put slightly more or less than 5 quarts in the jug.
 
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I was just reading through an oil change thread in the Focus ST forum, and different people get different results on their dipsticks when they claim to have added exactly 6 quarts to the same engines. Not sure how this is explained. Maybe if it's done on a lift, the car wasn't lifted completely level, and the oil pan is tilted opposite the drain plug? Impatient oil changers leaving old oil in, mis-shapen oil pans, or inconsistent dipstick length are my only other theories.
 

Benzadmiral

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I was just reading through an oil change thread in the Focus ST forum, and different people get different results on their dipsticks when they claim to have added exactly 6 quarts to the same engines. Not sure how this is explained. Maybe if it's done on a lift, the car wasn't lifted completely level, and the oil pan is tilted opposite the drain plug? Impatient oil changers leaving old oil in, mis-shapen oil pans, or inconsistent dipstick length are my only other theories.
It occurred to me that maybe his oil change guy left the old filter on -- but no, that was a blue AC Delco, and the black Mobil 1 filter with the logo is clearly visible in the engine compartment now. It was done on a lift, at that.

Well, if this is analogous to a BITOGer leaving his oil filter in place for 2 OCis, and thus leaving some older dirtier oil in the engine to be mixed with the fresh after a change, I guess there's no harm done. I just have a quart of good makeup oil for the future. (Though the LaCrosse is not an oil consumer, so I haven't had to add any oil.)
 
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