Maybe I missed it; immediately prior to changing your oil did you see any indicated oil level on your dipstick?

Just going from what I've heard, I think your extended oil change intervals, and using conventional oil, could be at least partly responsible for your oil rings sticking to the pistons, and the loss of oil. I would say to try a synthetic oil, but that might actually increase the loss at this point. Are you using 5w-20?

I'm using 5w-20 oil all the time. Do you think could there be a scratch along the cylinder wall? that collecting oil at certain stroke?

You didn't answer his question (or mine for that matter). Are you using conventional oil or synthetic? And did you check the dip stick immediately prior to changing the oil?

oh. I'm mostly using conventional oil. Yes, I did check the dipstick immediately before and after changing the oil. The amount collected on the dipstick only at few before changing. After change, it look normal.

What does that mean?

I've heard of some engines with scored cylinder walls, but stuck oil rings seems to be more common. Don't know what you could do to find out for sure. Compression test? Leak-down test? There is a camera that can enter the cylinder through the spark plug hole, and take pictures of the inside the cylinder walls.

At this point I'm thinking leak down tests and bore scope tests are way premature; as I understand it the OP's engine is only consuming a quart of oil every three to four thousand miles; pretty normal from my perspective.

I'm seeing it at half between max and min level

i think i see your confusion, you are interpreting the quantity between the max and min levels incorrectly. it is only one quart, not the entire crankcase capacity. ....say yes????