I've experienced the exact same issue. I ve been using 5w30 conventional. I started to add a quart between oil changes as well. I've been ok so far (136K to 163K).

 

Yeah I've had to check my 03 Maxima once a week,then I switched to 10W40 Synthetic with oil catch can and now I'm adding 1/2 qt and beat the **** out of it,my HR checked it couple of times not a issue at all,and before I switched to 10w40 with the Max I was like 1-1,5qts per oil change.

 

Guys at the lube goon place say they don't even bother to check the dipstick after they change the oil because the car has to sit so long. They put in exactly how much it calls for. Checked it the next day, exactly on the full line.

Now that I'm 1000 miles into my first oil change, the level was a little below the full line, took about 8 oz of oil to hit the line again. That's with about 90% stoplight to stoplight driving. I can live with it using a quart every 4000 miles.

 

My 2005 G35 6MT sedan with 117,xxx miles on it drinks about 1 to 1.25 quarts per 1000 miles or so. However, I don't really care because how much I like the car and how it drives (if it wasn't a high performance car I probably wouldnt give it as much love and care), I went out and bought a $17 5 quart Valvoline 5w30 Synthetic Blend bottle of oil and just throw a little oil in every 2 weeks to top it back up and everything is fine (that top up 5w30 oil bottle will last for probably about 6-8 months, I dont care about spending a extra $35 a year to top up my oil, whoopty do!), I treat my oil like my gas, every time I fill up (every 1-2 weeks, I dont drive that much), I top the oil up as well which is seemingly to be much cleaner throughout the duration than if I was using the original oil if it wasn't burning so I actually like this oil consumption issue because it allows me to manually keep cleaner oil throughout the engine throughout use versus older dirtier oil being continuously recirculated which makes reasonable sense that it would very slightly improve overall performance with this method by keeping the oil topped up and fresher consistently.

 

This isn't "Rocket Science" all anyone needs to do is check your oil level once a week! With a high mileage VQ motor keeping an eye on your oil level is an important as watching your gas gauge! I wouldn't go over 3K miles between oil/filter changes, going with 10W/30 synthetic might help if you have OC issues. Costco has a great price on Mobil 1 synthetic right now $10= off a case, 5 or 10W30 your choice...Gary