I own a 1997 nissan alitma. About three months ago, I had an oil leak repaired after noticing low levels and puddles under my car. A few months later however, I am noticing low oil levels again. However-there is never a puddle under my car. This is very odd because I'll put nearly a whole bottle of new oil in the car, and about two weeks later I'll barely get anything on the dipstick. I haven't seen the low oil light come on while I'm driving or any other time. I also haven't noticed an unusual ammount of smoke comming from my exhaust pipe. I thought that maybe the cold has been causing the oil to congeal thus giving me lower readings. However, it has been warming up and I'm still getting low levels. All I can think of is that the oil cap is kind of old and fits rather loosely. But, wouldn't that result in puddles or a noticibal ammount of fresh oil splattered under the hood?
BTW: My car has over 100,000 miles on it.

Put your finger and rub around the exhaust pipe, see if it's black or think black powder. That means that it burns oil a lot. Or if you leave the engine on and see if it has some blue smoke. Make sure about that first. Else I don't see how the oil can vanish.

93-97 altimas are notorious for leaking oil out of the timing chain seal on the left side of the engine, the seal needs to be replaced,this has to be done at the dealership they know the shortcuts and it should be under 300 if u dont want to spend that just keep on dumping oil in there like me...later

one of the service managers at the Nissan dealer here in Des Moines quoted me a price of $1,200 to fix the timing chain seal leak. Does this seem excessive?

thats way too much,call around to different places, shoot for that, u could buy a new engine have it installed then still have 100 dollars in ur pocket...

Resealing a front timing cover is a all Labor Job. I have done my fair share and take a half a day or more to complete. As far as the loosing oil condition. I didn't hear if you saw any leaks or anything wet under the vech . It is possible to have and oil leak and don't see anything on the ground. Dirt and oil can build up a sludge like material witch will just constantly absorb the oil until it is soaked. Make sure the engine is completely clean underneath and i would check it once a week .. Weekend type of deal.. Gl