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Oil just gets better and better?

On another forum I said I’d never use oil for more than a year, even though I only drive 4000 miles in that time and here is part of a response I got:

""Wear rates are actually still going DOWN in many examples, at 10k miles. The SAE study I reference even shows that wear becomes almost zero (not absolute, but darn near) when the lubes get aged. I realize that it’s hard to believe, but there are multiple SAE studies and lots of UOA data to prove this. Unfortunately, the mass-market sales hype is far louder and broader than I would ever be.

Also, it’s not that the engine is really being harmed by short OCIs; that is not borne out by the data. … What is being harmed is the wallet! Why dump oil at 3k or 5k miles, that is capable of 10k miles? You can change oil at 2k miles, but your wear rate is HIGHER than at 10k miles by far."


(I agree that choice of oil change interval, like choice of lover, is a very personal thing.)

I’d be concerned that the aged oil might settle out sediments if left in the car too long, and cause sludge which can be difficult to remove. I doubt keeping it the car for a year would be of much concern though. It’s probably best to follow the owner’s manual, which often gives a mileage and a time for changing, whichever comes first.

For you the issue is that the oil sits in the car with almost no use, absorbing moisture and not really getting hot enough to dispel the water. This water sits on your metal parts in very small dots, making very small pits here and there in the engine. The reason in your case to change the oil is time and not miles. You would have cheaper oil changes with regular oil every six months.

Oil ages when it is open to air, gets hot (molecules break down), is exposed to friction (molecules get “sheared” and break down, and when combustion contaminants (water is one, soot is another) get into the oil. I’m not sure what the oil in these “tests” was exposed and for how long, and if they are talking about regular oil, synthetic oil, or some blended mixture of oil.

Motors run much “cleaner” now than 15-20 years ago perhaps extending the oil change interval will be OK. However motors also run hotter now to reduce pollutants. Motors also run lighter weight (thinner) oil to reduce internal drag and friction, thinner oil is more likely to shear at a faster rate. If your motor has a turbo charger then the oil is stressed much more than the same oil in a conventional (non turbo charged) motor.

If you want to risk your motor to an expensive repair you can go for a long oil change interval, how about 10 to 20K miles every 2 years? Certainly this will save money on oil changes. I’m not doing that but its your car and your money.

I change the oil in my cars at 5K mile intervals. I have a couple of low miles per year cars that I change every year if they don’t reach the 5K mile mark in 12 months of driving. I don’t feel comfortable going with oil change intervals longer than that at this time.

“For you the issue is that the oil sits in the car with almost no use”

I do drive long enough to heat and dry out the oil, but I only drive 2-3 times a week, not to work every day.

And I do change the oil twice a year.
I’ve considered going to once a year, but the cost difference is trivial since I DIY.

I really didn’t intend this to be about my oil change habits.

Maybe the oil is still capable of lubricating, but by 10K, especially in city driving and through a winter, it has accumulated all kinds of crud from combustion byproducts, blowby, possibly some metals from the engine that the filter did not catch, etc. Filters are pretty good, but they can only do so much, and the oil is obviously not protecting as well at that point as it did when it was new. Some engines that are known to have sludging problems have probably beaten the oil up pretty well before 10K and will be incurring deposits at this point.

I wonder if what is beiing interpreted as “aging oil” is actually “bearings wearing in” - that the change in bearing wear has nothing to do with the oil. I would need to see the actual test to determine this, but I have seen others do this sort of backwards reasoning.

Does this mean auto manufacturers actually know more about their engines than even the informed public? I think so. And it’s reflected in their oil change instructions in the owner’s manuals: change when the OLM says to. The OLM in our 2009 Cobalt doesn’t drop below 20% life remaining until about 10,000 miles (all highway driving; mostly 8 hours at a time). Even our van doesn’t get below 10% until 7000 miles or more, and that is driven mostly short distances. BMW has recommended a change interval of 15,000 miles for a while. If you use Mobil1 extended life oil, there are enough additive compounds to remove the corrosive chemicals.

The problem with blogs and other internet sites is that most are not vetted. That means that the author is not necessarily a trained or accredited expert and the article does not get any type of peer or editorial review. Because of that, the internet is not really the information superhighway that was promised but more of a rutted and potholed dirt road.

Even wikipedia has some issues here. If you look something up in wikipedia, check the bottom of the article and see if it has been reviewed by a credentialed source. Many are, but not all. And that is not to say that only articles with credentialed authors and peer or editorial review have good information, its just that without these, you have to be careful, especially when an article goes against time honored and proven practices.

As for oil life, there are a lot of factors that affect the life of the oil. Those vehicles that have oil life monitors take in most, if not all of these factors. Without an oil life monitor, it is at best just a guess. Drive cycles are one of the most important factors in the life of the oil. That is the heating up and cooling down of the oil.

Every time you shut down your engine, there is a heat spike inside the engine as it dissipates internal heat when the coolant and oil is not being pumped through the engine. The oil trapped in the passageways and on top of the head take the worst of this and this is when thermal breakdown peaks. Hours of operation are the next biggest factor, that is where breakdown from sheer occurs as well as some thermal breakdown.

Many time, the time factor on oil changes is based on the normal number of drive cycles, about 28 per week) with the assumption that the drive cycles are just very short. In your case, your fewer miles are due to fewer drive cycles so you can safely extend your time interval. Once a year should be adequate for you.

I think the author sounds like an Amsoil salesman.

We don’t worry about gear oil in our transmissions and differentials so much because the oil there will never be exposed to contamination from unburned fuel and combustion byproducts, but whoever came up with the concept of motor oil getting better as it ages must belong to the same group of people who start urban legends because they have a sick sense of humor.

Look, for example, at the urban legend about being able to unlock your car by using a cell phone to transmit a signal from the key fob miles away. Whoever started that myth is a sick jerk who enjoys taking advantage of the gullible for no other reason than “because he can.” There is nothing to gain from it other than the perverse pleasure of knowing there are two idiots somewhere trying to transmit a key fob signal over a cell phone wondering why it isn’t working, and there are idiots spreading the myth who, if they thought about it for more than two seconds, could see why this idea is complete idiocy. This guy telling you oil “gets better as it ages” either has a sick sense of humor or has fallen prey to someone who has a sick sense of humor.

Look, for example, at the urban legend about being able to unlock your car by using a cell phone to transmit a signal from the key fob miles away.

Someone took a little knowledge about On-Star and then illogically extrapolated the next step by using ones cell-phone to do the same functionality. On-Star is basically a on-board cell phone with a few other features (like crash detection). It’s also directly connected to the cars engine computer and the electronic door locks. Your cellphone ISN’T.

Hey, I’ve got a fortune in pre-conditioned oil for sale, if the price is right!!

The other issue with the cell phone example is that they have tremendous amount of filtering going on so that only the speaker’s voice is captured and transmitted to limit bandwidth requirements. Try hearing some high pitched noise through your phone sometime…assuming the speaker/pre-amp could even pick up RF that is :wink:

“You can change oil at 2k miles, but your wear rate is HIGHER than at 10k miles by far.”

Huh? I beg to differ. I’d be interested in hearing the explanation as to why your wear rate would be far higher by changing your oil every 2,000 miles than every 10,000 miles. 2,000 miles is IMHO obsessively often, but your wear rate would not be higher.

Circuitsmith, where di you get this balogna?

It is true. Under normal conditions new motor all will give slightly less mileage than new.

I’d be interested in seeing some theory to back that. Or at least some test results.

“Under normal conditions new motor all will give slightly less mileage than new.”

I can buy that, based on viscosity changes and shear thinning.
But new oil increasing wear?

TSM: this came from “Bob is the oil guy”, where else?

I could buy the argument that when you change the oil every 3,000 miles, the first time you start the engine after putting new oil in the engine, the oil light will stay on for 3-5 seconds as the new oil circulates through the engine, causing a slight amount of engine damage. The argument that this damages the engine more than leaving the oil in there an additional 2,000 miles (and changing it every 5,000 miles), seems plausible and reasonable. I wonder if that is what the author was going for.

Thanks Circuitsmith. I’ll have to do some research on this. This is that first time I’ve heard ti.

I believe the source of this came from a guy that decided to see how long Mobil One would last in his brand new Camaro. He took an oil sample every 1000 miles and had it tested. In addition, he changed the oil filter every 6000 miles and added a make up quart.

I think he was keeping a blog on Bobistheoilguy site and at 18k miles, he changed the oil to a different synthetic to see if the results would be the same. I did not follow up so I don’t know if he kept posting, I only read the blog once at the 18k mile mark.

He made a lot of assumptions based on the oil test results and what he had heard form other people, I have no idea of the qualifications of any of them to make these assumptions. One of the things the lab tests found was that the lubricity of the oil increased during the first 3000 miles, and then remained steady except for a slight dip each time the filter was replaced. Another thing that seemed to follow the increase in lubricity was the increase in dissolved metals. It followed the lubricity almost one for one.

The assumption was that the dissolved metals somehow increased the lubricity by acting like tiny ball bearings. When the oil reached saturation level of dissolved metals at around 3000 miles, then it stopped dissolving metals and the lubricity leveled off. New oil would have less lubricity until it dissolved some more metal from the engine. DISCLAIMER here: this is from memory and the ideas expressed in this paragraph are not mine.

Anyway, as I said earlier, and this is my opinion, the internet is not the information superhighway is was promised to be but rather the mis-information dirt road.

I’m going to stick my neck out and post the thread:

In the past I’ve had posts removed from CarTalk for doing this.

Here’s a link to the SAE study (but it’s not free):