2002 altima burns oil about a quart every 300 miles. I Just got this car engine is very clean . I had oil changed and they talked me into haveing an oil flush ran through the engine with the oil change. They said it was a mild dergent type flush. I have not had the car very long so I dont know if it burned oil before that point. But as i said I know it burns it about every 300 miles now. What can I do

Rear or front main seal.

we check oil every other fuel fill up. on old cars, every fill up
did you run car 10,000 miles to a oil change? unstated.
1qt/3000 miles is perfectly OK.
so 10000 mles is 3.3 quarts burned and off the top of the dip stick
if you drive fast, it burns more, got a heavy foot, or load in back>?
if you had done it right, you'd have already learned YOUR engines
consumption rates, and learned to check when IT , needs checking
we do this on all engines. all machines.
all engines burn oil, the exception , a church car, new, and never driven, far, or fast or for 10000 miles to an oil change.

your mech, was right, he was thinking , you dont check oil?

Whenever I encounter an engine that's missing oil I always start with the basics. First I take a good look underneath and check for any drips, no matter how small, as a leaky sending unit, oil filter, or cooler line won't leak once the engine is off. If you can park on the same spot, preferably over a clean piece of cardboard, it makes it a lot easier to spot any drips. If no drips are present then I change engine oil and filter using a top grade oil and fill the level to exactly the full mark on the dipstick. I do this because most engines will burn oil if the oil is dirty and old enough. At that point I check the oil every 100 miles or so [after the engine has been off for a few minutes] and see how long it takes before the engine is a quart low or down to the "Add" mark. Once you have this information then you can decide what or if you need to do anything. As for what's normal oil consumption? Most vehicles won't use a quart in a 3,000 mile service interval but I've seen new vehicles that take a quart every 1000 miles or so, thus there's really no good solid answer although I think a quart per thousand is excessive...but often expensive to fix if it's actually burning it. Hope this helps and good luck!

if it is not leaking then it is being burned by the engine, how many miles go by before you need to add oil?, if u are adding more than one quart every 1000 miles u have piston reing problems and or valve guide seal leaks. U won't see any smoke in most cases unless you are really going through the oil, like 1 quart every 300 miles.

It is not normal for a car with 29,000 miles on it to consume this amount of oil in 10,000 miles. We usually change our oil between 3 and 5 thousand miles and thus may not notice small amounts consumed but certainly not 1-2 quarts. It is more likely that you are leaking oil, but if it is burning it, that is a real problem. If the car was pre-owned do a CARFAX. If it was wrecked, find out was was done. If the odometer is correct, this car needs to be inspected by a professional. I can tell you to look for unburned oil in the tailpipe, smoking exhuast, leaks from the oil pan and drain. Change the oil and filter and closely monitor the level.

Its 3 1/2 Quarts, but you might as well put a full 4 quarts in if it goes through that much. make sure you change the filter aswell! dirty oil will not cause your engine to go through it any faster. Is the oil leaking or is the engine burning it?

If you love the car as you say than be prepaired to shell out the bucks for a rebuild or replacement engine, because thats the only fix for your situation. You may not see any blue smoke but believe me its burning it, or you got a leak witch you say you don't. Its going someware and most likely its out the exhaust.

check engine light has nothing to do with oil level. Only the red engine light does. It sounds like you are burning a lot of oil and it is poisoning your catalytic converter. Your converter is killing itself trying to treat all the unburned oil that is coming to it. It will get so hot that it swells inside and clogs it up. Why you are burning oil is the question. Only 3 possibilities. Past the piston rings, past the valve stem seals or a plugged pvc valve and its hoses. Clean the PVC hose and change the PCV first. Changing the cats now will just kill them again until you fix the oil burning.
Autozone will do free scan test for fault codes by the way.
PCV won't show up there though.
You can buy cheap engine on ebay or at car-part.com. page with asterisk is lowest price.

Check out this thread and take your Caddy for a couple of Wide Open Throttle runs on the Interstate. Clears out the carbon buildup on the rings that is causing oil blowby.

http://townhall-talk.edmunds.com/direct/view/.f1078f6/0

yeah ive seen this a lot on the altimas!! headgaskets leak to nissans are turning into garbage