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2003 Maxima SE - Hearing rattling from engine and starting to go through oil quickly

I own a 2003 Nissan Maxima SE with a 6-speed manual transmission. The car has just under 113,000 miles on it. I’ve religiously maintained the vehicle per the owner’s manual and overall it is in excellent condition. In particular, we change the oil on a regular basis per the maintenance schedule. However, on several occasions we have started to hear rattling coming from the engine. The rattling occurs at all engine speeds and in all gears and it doesn’t matter whether the car has just been started or if the engine has been running for a while. When the rattling has gotten more prominent, we’ve taken the car to the dealership and also to our local oil change place and on both of those occasions, they’ve told us that the engine oil was VERY low. Also on both of those occasions, we were well within the recommended range in between oil changes (<3000-3500 miles). We have not noticed leaking oil in our driveway or in our garage. I am wondering about the potential reasons why we could be losing oil, and if we aren’t seeing any in our driveway where it’s going? I’ve mentioned this to friends and they’ve said it’s ‘burning oil’ - but we’re not noticing any strange smells or smoke. Is there a suggested recommendation about how to diagnose and fix it? The car is ~10 years old but it’s fun to drive and in great condition so I have no interest in selling it if I don’t have to.

You are not seeing any oil smoke because the catalytic converter is eliminating it. However, this will continue only to the point where the CC becomes burned out as a result of the overload of oil in the exhaust stream. You need to get to the bottom of the problem a.s.a.p. if you want to avoid replacing that VERY expensive CC.

That being said, your biggest mistake was apparently not checking the oil level between oil changes. It appears that–no matter what the cause of the engine’s oil consumption was to begin with–you exacerbated the problem by failing to monitor the oil level.

If it has gotten to the point where the engine is making rattling noises, that means that damage has already been done, and then the question arises of whether it is worth tearing down an engine on a car that is 10 years old.

My best advice is to begin by changing the PCV valve and the hose leading to the PCV valve. This might (or might not) reduce the oil consumption. If that does not help, then if you don’t want to invest big bucks in an engine that is “damaged goods” you might want to use an oil additive that is designed to reduce oil consumption. Some of these products, such as Restore, do actually work, at least to some extent.

With this car, and with your next car, you need to get into the habit of checking the oil dipstick at least every couple of weeks in order to avoid damaging the engine.

If I understand correctly, you don;t check your oil level between oil changes?
And on at least two occasions, each after some 3000-3500 miles, the engine has been found to be VERY low on oil?
And, you’ve continue to drive the car after it begins rattling until the rattiling became prominent and then you’ve taken the car in to the shop…wherein you’ve been told it’s VERY low on oil?

Chances are excellent that you’re burning oil. And the odds are that you’re burning a lot more than you would be had you been checking your oil level regularly and adding a quart when needed. Driving a vehicle that’s low on oil means that whatever dilutants and contaminants are suspended in it are suspended in far less oil than they should be. Meaning the oil is far more contaminated and diluted than it should be. That manifests itself as far more wear on the engine’s insides.

You can diagnose it with a compression test. That’ll give you an idea how worn the cylinders are. It’s probably sludged up too, but you’d need to pull the valvecover to assess that.

It’s had a hard life. At this point I’d be inclined to get some additive at teh parts store and clean the sludge out of the oil channels, and then get it filled with fresh oil and monitor the level. Whatever danage has been done would require a rebuild to correct.

The word “religiously” and factory maintenance schedule does not always go hand in hand. You state the oil changes are at 3-5k miles intervals and that may or may not be good enough depending on the driving habits and conditions. Your car has comparatively low miles on it for being 10 years of age so that does point to possible severe service.

Running the engine low on oil is not only damaging to the engine but can also contribute to oil sludging problems which in turn can lead to oil consumption. You really need to develop the habit of checking underhood fluids every couple of weeks at most.

At this point a compression (both dry and wet) or leakdown test should be performed to test for any possible piston ring problem and an oil pressure test with an external gauge can help to determine if the lower end is worn.
My gambling money says that the results of those tests combined with the knocking noise means your current engine is on a bad downhill slide and you should start planning for the future along with not venturing on any extended trips.
Depending on the severity, knocking can eventually lead to a loud bang when a bearing shell spins or rod bolts break. At that point you will be dead in the water.

Changing oil as per the manufacturer’s recommendation and checking the oil level are two different things. My wife rented a Ford Econoline van from Rent-a-Wreck some years back to take a high school church youth group to a work camp about 400 miles away. On the dashboard of the van was a big sticker that read “CHECK OIL AT EVERY GASOLINE STOP” Now, my wife didn’t have to add any oil, but I still think this was good advice. Our son drove a small school bus for a day care center one summer. He was required to check the oil, the coolant level, the transmission fluid level, and the brake fluid level as well as all the lights every morning before starting his route. While all this fluid checking may seem excessive, I check the oil, glance at the coolant reservoir and the brake fluid reservoir once a week. I do this when the engine is cold. It takes less than two minutes to make these checks and my vehicle is a 2011.
Whether you rebuild your engine, replace it with a remanufactured engine, or replace the entire vehicle, get in the habit of checking the oil once a week. Keep a quart of the correct oil handy so that you can top it up. This 2 minute investment of time will pay dividends. As a side note, I check the oil on my lawnmower every time I get it out to cut the grass and I have used the same lawnmower since 1988.