# Just change filter?

My 1999 Nissan Altima uses (leaks) about 1 quart of oil every 1000 miles. My last oil change was 5000 miles ago, and I typically change oil every 5000 miles. Right now though, since the engine is constantly being fed a quart of “fresh” oil every 1000 miles, the average “age” (in miles) of the oil in the car is decreasing, unless I’m making a serious mathematical oversight. The car holds about 4 quarts, so here’s my logic:

1000 miles after oil change: 3 quarts remaining with age of 1000 miles and 1 quart added. Average age of oil = [1000(3)+0(1)]/4 = 750 mi.
2000 miles after oil change: 3 quarts remaining with (average) age of 1750 miles and 1 quart added. Average age of oil = [1750(3)+0(1)]/4 = 1313 mi.
3000 miles after oil change: 3 quarts remaining with (average) age of 2313 miles and 1 quart added. Average age of oil = [2313(3)+0(1)]/4 = 1734 mi.
4000 miles after oil change: 3 quarts remaining with (average) age of 2734 miles and 1 quart added. Average age of oil = [2734(3)+0(1)]/4 = 2051 mi.
5000 miles after oil change: 3 quarts remaining with (average) age of 3051 miles and 1 quart added. Average age of oil = [3051(3)+0(1)]/4 = 2288 mi.
… etc.

Carrying this out “to infinity,” it turns out that the average age of my oil will “top out” at an age of 3000 miles. The average age of the oil in an engine that uses NO oil and gets an oil change every 5000 miles is 2500 miles, so I’m considering not bothering to change OIL any more, but just change the FILTER every 5000 miles! Thoughts, anyone?

All you’re doing is diluting the oil. I’d still consider changing it though. Maybe you can increase the interval to about 7k miles…but I’d stick with the 5k miles.

Sorry, but it doesn’t work that way. The oil is still ageing and should be changed on schedule. Of course if you no longer car about this car and want to go cheap on maintenance you can skip oil changes. Just expect the oil consumption to increase and the tired motor to not last as long.

You seem to be approaching the “run it into the ground” stage of the car’s life and skipping oil changes will just hasten it’s demise.

I agree with your mathematics. But rather than abandon oil changes altogether, I recommend you extend the interval instead. After about 7500 miles, get an oil change when your car is about one quart low.

There is validity to what you are suggesting. A few years ago I learned on this site about the existence of the Cummins Centinel diesel engine oil change system. You can search to read more about the system. I have not been able to find any specifics regarding the rate at which it feeds engine oil into the fuel supply but a truck driver might be able to tell you how much oil is added to the fresh oil supply tank for a particular distance driven as it relates to crankcase capacity. With that information you might be able to form a reasonably good oil change mileage estimate.

But doesn’t a used engine introduce more blowby gases, etc into the oil? Meaning that a worn engine is a dirtier engine, and “average 3000 mile” oil might be much dirtier than you’d expect.

If the loss were due exclusively to leaking seals, I’d be happier with the ploy.

I’d recommend changing on the regular schedule, but using the cheapest oil (with API rating) you can find. That should be about \$12/gal, or less, if you shop carefully.

If you can’t afford that, can you really afford to drive at all?

The only way this makes any sense is if you’re changing the filter yourself at home and throwing it in the garbage. Otherwise I can’t see how it would save you any time, effort or money.

The only benefit I can see to not changing the oil anymore would be that you are reducing the amount of oil that you are putting into the wastestream for recycling or disposal. But since you leak a quart every thousand miles directly into the water supply I don’t think that’s your motivation.

I’ve done what you’re proposing, I’ve seen others do it, and it’s worked fine.

It’s a 15 yr old car. How long do you plan to keep it?
If it’s for many more years, then fix the oil leak.
Else, just change the filter as you suggest.

Where is the leak?

I guess in theory that if you change the oil filter more often, say every 3000 miles, and you’ll lose a quart at that time when you spin it off . . . and add fresh oil every 1000, you theoretically you’re cleaning your oil with a new filter all the time and adding the additives with the new quart every 1000 miles. If it were mine, I would fix the leak and go back to regular maintenance schedule. Rocketman

Years ago there was a Franz Oil Filter on the market which used a roll of toilet paper in a canister that held 1 quart. The claim was you never needed to change oil; just change the filter every 1000 miles. With a 4 quart crankcase that meant you were constantly changing the oil, and one driver claimed 100,000 miles with the engine still performing well. That was probably just highway driving.

Although there is some merit to your calculations, an older engine has more blow-by and the oil contaminates faster. I would change my own oil and filter at about 5000 miles, if possible and use the cheapest Walmart oil that meets your spec. Recyled of the right spec oil would be good as well. I have done this in the past with some older beaters and got easily another 3 years out of the engines.

Large industrial engines have big oil sumps and the oil is centrifuged, degassed and filtered constantly to keep it clean. Its condition is also monitored regularly for acidity, viscosity and other qualities. Once a year the oil may be changed and a barrel or so of fresh oil installed. This type of operation is not feasible for moving vehicles, so even large trucks with big sumps need regular oil changes, although the interval is much longer such as 20,000 mile and up.

Wow. Quite a variety of opinions. Reminds me of congress.

Anyway, I just changed the filter only (Puralator Pure 1–woot!) and added about 1.5 qts to bring it to the full mark. I’m not sure why some of you are assuming this engine is near its end. It only has 160K and it’s a Nissan.

Should I be more concerned about the leak? I’m not concerned at all, really. It would obviously be nice if there wasn’t a leak, but 1 qt/1000 miles isn’t very costly. Oil is more expensive than it used to be, obviously, but it’s still relatively cheap. Compared to gasoline expense, for example, it’s a drop in the bucket.

Aside from the pollution aspects of this mentioned before, you might want to make sure the oil isn’t dripping onto an exhaust manifold or pipe. (fire and all that.) If the leak is from the valvetrain covers, you might want to consider fixing it. I mean, essentially what your doing is the same as stopping your car by the side of the road every 1,000 miles and pouring a quart of oil onto the ground.

@ccsluf: We’re assuming the engine is on borrowed time due to high oil consumption. Oil-burning is the hallmark of a tired engine. 160k is pretty darn high for an engine, too…probably 80th perctentile for engine life. And what does it being a Nissan have to do with anything?

If you really want to know engine health, have a compression test performed.

And I don’t understand: you brag about using high-zoot filters, but you’re unwilling to pay an extra \$10 for 3 additional qts of oil. To which I say: you’re simultaneously employing two incompatible maintenance philosophies with your car. You’re wearing beach sandals with your tuxedo, if you will, which puts you out-of-place anywhere. To extend the metaphor, you need to decide if you’re headed to the beach or the opera, and dress accordingly.

@DrRocket, “I mean, essentially what your doing is the same as stopping your car by the side of the road every 1,000 miles and pouring a quart of oil onto the ground.”

I don’t understand how that concept escapes so many people. I’m far from a greenie tree-hugger, but where do they think that oil/coolant/fluid goes? I had a guy working here for a while, he had a Toyota with a leaking oil pump gasket. He could buy oil at cost, so the fact that he used a quart a day didn’t seem to bother him. I reminded him that what he was doing was the same as just pouring a quart of oil into the bay every morning. He still didn’t fix it. One day I had him bring his car in “on the clock” and fix it so I wouldn’t have to see that leaky pig every day.

Here at work, one guy’s truck leaked so badly, they actually kicked him out of the employee parking lot until he got it fixed. He was pretty upset about it, but did get it fixed. He later (begrudgingly) admitted it was nice not having to fiddle with putting more oil in all the time.

I think I’m gonna make my first million by patenting a system that takes some small % of the oil pump’s output and diverts it into a spray-bar system running under the car. You never have to change the oil, AND your vehicle never rusts! (Of course, your parking spot will eventually look Valdez-esque, but hey: 2 outta 3 ain’t bad!)

Continue to change the oil at 5k to 7.5k miles…or fix the leak. Leaking one quart of oil very slowly does little to get Rid of the accumulated contaminants. Sorry to disagree with most, but there is no logic to you actually getting away with no oil changes or just changing the filter. You mistakenly confuse oil age with it’s ability to hold contaminants. The oil already in there immediately contaminates the miniscule amount of fresh oil so the motor never gets the benefit of bathing in fresh oil from ground zero or oil never suffering from thermal breakdown. Theoretically, two stroke motors operate on this same principle…but theoretically, their engine wear is much greater too and they polute. You too are poluting the environment. And people get after some for poluting for spraying oil ( one quart) into the body cavities for rust prevention, once every two years over newspaper. Good grief ! ;=)

You know, this oil leak might be easy and inexpensive to fix, especially if it’s something like a valve cover gasket. Not changing the oil is something you do to your car when you want it to die because you’re sick of it and you’re too lazy to sell it and buy a new one.

You can keep polluting the environment with empathy-induced oil, but I recommend you get an estimate on fixing the leak. Most cars of this generation can last well past 200,000 miles if they are properly maintained.

Just adding oil is similar it Honda’s recommended method of changing transmission fluid. They instruct you to drain and fill 3 times when you change transmission fluid. If you are comfortable with the analogy, then just change the filter and add your 1.5 quarts to make up for the filter loss, at least over the short term. It makes sense to at least determine whe the leak is. If it is something simple like an oil pan gasket, changing it could extend the life of the engine by reducing the risk of a larger, more dangerous leak in the same spot. You can’t predict when or how much the leak will grow.