Dear Tom and Ray:
I have a 2002 Nissan Altima that for the past six months has been losing oil at the rate of about a quart per month. I thought that it might be either leaking oil or burning oil. However, there are no drips under the car, and it recently passed emissions testing during inspection (I would have thought it would have failed if it was burning oil). Anyhow, I'm perplexed. What's happening to the oil? Otherwise the car runs fine, and the gas mileage is as it always has been. When the oil starts to get low, I notice a slight metallic fluttering sound in the engine. When I top off the oil, that goes away. Is this a sign of serious engine problems? Thanks!
Ray: For some people, losing a quart of oil a month is a serious engine problem. For my brother, losing a quart every 10 minutes is but a minor inconvenience.
Tom: You're burning the oil, Mike. If it's not leaking, you're burning it. Burning oil won't necessarily cause you to fail an emissions test. Most emissions testers measure carbon monoxide, carbon dioxide and unburned gasoline. There's no "engine turning to crap" oil-burning detector in the emissions tests yet.
Ray: And that's a lucky thing for you! Either your rings are shot (big, big money), or you have worn valve guide seals (medium money).
Tom: The "metallic fluttering" sound you're hearing is your engine suffering from oil deprivation. My guess is, it's either the lifters collapsing, or it's the timing-chain tensioner letting the chain slap against its cover -- neither of which is good.
Ray: So you have two choices, Mike: You can have your mechanic start taking apart the engine (and pray for bad valve guide seals), or you can keep a close eye on your oil level, and just keep driving.
Tom: That's the option we thought you'd pick! If you decide to just keep driving it, from now on you have to learn to add the oil before you hear those noises.
Ray: So Step 1 is to check the oil more often. Once a week is good, for now. And check it in the morning, before you start the car. That way, you don't even have to wipe off the dipstick. You just pull it out, have a look and go.
Tom: Step 2: Start adding oil when you're half a quart low. That should keep those key parts from being deprived of the oil they need to work correctly.
Ray: Finally, keep changing the oil regularly. A lot of people make the mistake of thinking that adding oil is a substitute for changing oil, but it's not. In fact, when your engine is regularly running low on oil, the remaining oil is working even harder. Three quarts are doing the work of four. So that oil needs to be drained out and replaced more often rather than less often.
Tom: The oil burning will eventually get worse, Mike. At some point, it'll become unsustainable -- unless you move to Saudi Arabia and drill your own backyard well. But if you're careful, you probably can keep this car going for a good long time. Best of luck.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk Web site.)