Time-based oil change

[avanti]

There are few truisms more ingrained in the auto industry than the need for frequent oil changes. For many years, the rule was "three months or 3,000 miles". The advice has evolved over time, and the milage recommendations now generally range from 5,000 to 20,000 miles. Lots of people are skeptical about these recommendations, but if you dig deeply enough, it is possible to find the science behind them.

Not so for the "time" part of the rule. Current recommendations are usually in the 6-to-12 month range, but as far as I have been able to determine, there is little or no science behind these numbers. Searches will uncover reasons like "because oil deteriorates over time" or "oil looses viscosity when it sits" or "the additives degrade" or "water accumulates and damages your engine". If there is actual evidence for any of these claims, I have been unable to find it. For this reason, I have become somewhat skeptical of the importance of time-based oil changes.

Courtesy of the Covid crisis, I was recently presented with the opportunity for a "natural experiment" on this topic. I own a 2007 Toyota Highlander, which has spent its life at our vacation home. We keep it at an open, but well-covered parking spot in the Desert Southwest. We typically use it for local service a few weeks every few months. Before the pandemic, its last oil change was done on Aug 22, 2018--mileage was 31,405. When Covid hit, we had put about 3,500 miles on top of that. Then it sat, undriven, for more than two years. When we finally rescued it and took it in for an oil change, it was July 7, 2022 and the mileage was 35,155. So, at the time of the oil change, the oil had clocked 3,750 miles and was nearly four years old.

This was a perfect opportunity to call the "old oil" question, so I had the oil-change guy take a sample and I sent it out to Blackstone. I even spent the extra $10 for the optional alkalinity test. Here are the results:
BlackstoneReport.jpg

Bottom line: I can find zero evidence that the oil in this engine wasn't perfectly serviceable, or that it suffered in any way from its long sleep. Of particular interest is "TBN", which is what I got for my $10 extra. It is a measure of alkalinity, which is present to neutralize the tendency for oil to become acidic in use. Values < 1.0 are problematic. Mine was 3.5. Viscosity was also fine, and the other additives are apparently just fine as well.

Only one data point, but a pretty good one. (It was even sort of a blind analysis, since Blackstone had no idea how old the oil was). Reach your own conclusions. I have reached mine.

P.S. -- In case you are wondering, when we rescued the vehicle, I flipped my battery disconnect switch, turned the key, and drove off as if I had parked it the day before. So much for the "battery self-discharge in 3 months" theory.

[Doneworking]

That is great information. I had always suspected that was the case but now thanks to Avanti the lab has provided confirmation of our assumption.

Remember: the oil changing world has to change oil to have change in the till.

[booster]

I will add a bit of back story to all of this, based on my opinions and experience.


First off, oil does not deteriorate on it's own just sitting.


Second off is that some types of engine damage are not immediately visible and will not show up on an oil analysis.


From what I have been able to research, the automotive industry have abandoned the previous gold standard TBN (total base number) in oil analysis to focus more on the TAN (total acid number). I think this is a good idea. Changes in fuel and engine controls have dictated this change.



From what I have seen over the years of tearing down engines is that the ones that sat the most also had the most lower rod and main bearing shells that showed the most pitting and erosion. This is commonly caused by high acidic content of the oil. The longer it sits, the more pitting, so makes a lot of sense to me.


Bearing shell pitting and erosion usually will not show up on an engine analysis as it is a slow process, but will over time cause issues. Eventually the erosion starts to increase the bearing clearance and that reduces the oil pressure, and we all know where that leads. Eventual increased wear and engine failure.


This said, I don't believe in fixed oil changes based on time, especially if the vehicle is driven regularly. I do believe that if a vehicle is going to be stored for extended amounts of time, the oil should be changed before the storage. To me this is just common sense if you plan to have the vehicle a long time as what you do now may bite you 5 years later in lost oil pressure.


I have followed this idea for all the time I have had summer driven hotrods and now our van. I have torn down two of the hotrods engines to inspect and modify and they showed no erosion or pitting in the bearing shells, so I am inclined to believe that the oil changes made that happen.

[avanti]

I am far from an expert, but a few questions:

1) I understand that TAN is a more direct measure of oil quality than TBN, but aren't they inversely related? I.e., doesn't a high TBN basically preclude a dangerously high TAN value? I can see how a low TBN isn't necessarily damning, but how could there be high TAN in the presence of adequate TBN?

2) How is it possible for pitting and erosion to take place without it appearing as high metal values in the oil analysis? The metal atoms have to go somewhere, no?

Not trying to make any particular point--just trying to learn.

[booster]

Originally Posted by avanti

I am far from an expert, but a few questions:

1) I understand that TAN is a more direct measure of oil quality than TBN, but aren't they inversely related? I.e., doesn't a high TBN basically preclude a dangerously high TAN value? I can see how a low TBN isn't necessarily damning, but how could there be high TAN in the presence of adequate TBN?

2) How is it possible for pitting and erosion to take place without it appearing as high metal values in the oil analysis? The metal atoms have to go somewhere, no?

Not trying to make any particular point--just trying to learn.

I had a lot of the same questions and dug a bit deeper. Apparently there are two kinds of acid that can build up and the TBN only is directly related to one of them. I am not an expert on that at this point, but it explains why the old inverse relationship doesn't work any more.


I also wondered about the wear particles and the oil analysis and it seems to be that the small pitting, now days of aluminum and not babbit are low enough to not make big changes in the analysis. Aluminum from the skirt on the pistons probably is more. But it does accumulate over time and trap debris in the bearing which is not good.


Aluminum bearings have nearly doubled the life of babbit according to the shop that did my latest engine machining (high end racing engine shop), but what are the downsides?


With the new direct injection engines and their issues with cylinder washdown wear, we will probably see all this change again in coming years.


I found it very interesting that the Blackstone analysis didn't include TAN as that appears to be a big factor in current generation engines.


All of this is getting a lot more technical than "my dad did it this way", I think.

[avanti]

I guess I can see the "two acid" thing, but the chemistry isn't obvious to me.

But, I dunno about this idea that there could be visible pits that don't show in the analysis. Doesn't seem plausible to me.

Originally Posted by booster

I found it very interesting that the Blackstone analysis didn't include TAN as that appears to be a big factor in current generation engines.

They will do TAN for another tenner, but the website says that it's

not typically used for gas and diesel engine samples.

and

The TAN is mainly used for transmissions, gear oils, and industrial-type applications.

so I didn't order it.

[GeorgeRa]

My example is similar to Avanti’s one. We left Europe in October of 2019, our car was just serviced, parked in the garage inside the apartment house, full tank. It had about 2 km since the service. The car was untouched for 3 years and 3 weeks ago, we replaced the battery, engine fired in less then a second. On half low tires we drove to the nearest gas station to pump the tires. All OK.

We had to get the car inspected, mandatory once per year, that checked each wheel brake, parking brake left and right, suspension, steering system, lights, had some issue with 3 years gap but we passed. I asked about the oil, 3 years old, car parked in the indirectly heated garage (inside the building), about 15km since oil changed and the dealer answered to wait until the next schedule change.

[booster]

The two kinds of acids that I saw referred to were apparently being called to "industry speak" as hard and soft acids. I have not found an explanation for certain as to what they are in chemical terms, but did find this in an article about TAN measurement.

TAN testing is a measure of both the weak organic acids and strong inorganic acids present within oil

Several articles spoke of the soft acids being formed over time in the oil as it is used and the higher operating temps in modern engines contributes to that formation.


Traditionally, I would also expect to see the bearing erosion in the analysis, but that would be for old school babbit or trilayer bearings which would show up as tin, lead, and copper. With aluminum bearings the bearing wear can be masked by all the other aluminum parts in the engine that see oil, like the pistons, heads, intake manifolds, etc, I think.



Quite a few articles I read spoke of how in the past TBN was a good measure of oil life, but now they say that it isn't because they don't see increased wear products in the used oil go up when the TBN is depleted like they used to see. They specifically mentioned bearing erosion in a couple of the articles and were referring to copper, tin, and lead, so not aluminum bearings.


TAN has been part of the testing and a defining factor the industrial oils that I dealt with in the past, mostly from gearboxes, compressors, and hydraulic pumps, but engine stuff was all by TBN, it appears. Now there seems to be a big push to make TAN the defining factor in analysis for engine oils also.


From a practical standpoint it may make the oil be "acceptable" to continue using for longer than going by TBN depletion if they are right in saying low TBN doesn't necessarily mean more TAN or wear.

[GeorgeRa]

Originally Posted by booster

The two kinds of acids that I saw referred to were apparently being called to "industry speak" as hard and soft acids. I have not found an explanation for certain as to what they are in chemical terms, but did find this in an article about TAN measurement.





Several articles spoke of the soft acids being formed over time in the oil as it is used and the higher operating temps in modern engines contributes to that formation.


Traditionally, I would also expect to see the bearing erosion in the analysis, but that would be for old school babbit or trilayer bearings which would show up as tin, lead, and copper. With aluminum bearings the bearing wear can be masked by all the other aluminum parts in the engine that see oil, like the pistons, heads, intake manifolds, etc, I think.



Quite a few articles I read spoke of how in the past TBN was a good measure of oil life, but now they say that it isn't because they don't see increased wear products in the used oil go up when the TBN is depleted like they used to see. They specifically mentioned bearing erosion in a couple of the articles and were referring to copper, tin, and lead, so not aluminum bearings.


TAN has been part of the testing and a defining factor the industrial oils that I dealt with in the past, mostly from gearboxes, compressors, and hydraulic pumps, but engine stuff was all by TBN, it appears. Now there seems to be a big push to make TAN the defining factor in analysis for engine oils also.


From a practical standpoint it may make the oil be "acceptable" to continue using for longer than going by TBN depletion if they are right in saying low TBN doesn't necessarily mean more TAN or wear.

Hard and soft acids could relate to their evaporation, inorganic hydrochloric acid (HCl) or organic acetic acids (CH3COOH) will evaporate but sulfuric acid (H2SO4) will not.

[mkguitar]

Cool to see test results.
oil is cheap
I change it using quality product


I am just getting comfy with a 5000 interval on my newer vehicles.
I stay with 2000~3000 of my old carbed stuff
less than 3000 with modern motorcycles
close to 2000 for carbed motorcycles






I consider use; hot/cold, street or highway



and like fresh oil before storage/downtime




it's the acids formed which I worry about.


* i may cheat and not change filter if I consider the wear on the oil marginal.



oil is cheap, changing is easy especially on my van which I can do with it flat on the ground


I do consider oil change cycles before leaving on a long trip if going to the PNW from AZ, I may change oil before we go and know I can do the whole trip


On last trip I had 2000 miles on oil, planned a change at brother's driveway + 2300 miles, then another change at a parking lot 4900 miles after that ( oil no filter) and got home with about 800 miles on that oil, knowing the van will likely sit a few months

[Trav59KL]

First, I am a great believer in the adage that oil is cheaper than machinery. I do change oil regularly, and find modern extended change recommendations a little scary. I grew up in the days when the recommended oil change interval was one thousand miles.

However, what we called "oil" in those days and what we put in our cars today are very different. I think the modern extended intervals have been verified by a good deal of testing. Modern oils (particularly the synthetics) are more durable, chemically The molecules are not so easily broken down by heat, pressure and friction.

On the other hand, even if the oil itself is not degraded, a change can become necessary when it becomes contaminated...dust taken into the engine, condensation of water within the crankcase are two concerns that come to mind, and might be justification for an oil change even when the mileage interval has not be reached.

One final note: Some many years ago I read an article about a NY taxi company which conducted an experiment: they did not change the oil for lengthy periods of time....well beyond all normal intervals. They kept the oil levels topped off, but did not change out old oil.

At the end of the experiment, they opened up the engines, and micrometer measurements did not show engine wear outside of normal expectations. Of course, can you measure everything that might have been affected?

[Staggerwing]

Oil life is a hard target. It depends on your mission, environment, location, and driving behaviour. A GM 350 in an urban household Escalade, is a very different environment to a pick up in a logging camp in Alaska or a School bus. But the oil change info in the owners manual is the same for all 3. As long as the oil is still holding the by-products of combustion in suspension- it’s doing it’s job. Once the oil becomes saturated- it no longer holds on to the bad stuff and then it’s a science experiment.

The trick it to know your rig and get the ALMOST saturated oil out before it gets too late. How do you know - colour, smell, consumption are all keys. If you don’t know how to monitor this - stick with the recommended interval. Oil is the cheapest thing you will put in your rig except water.

The old wives tales of our fathers don’t apply - oil is better, fuel (nolead) is WAY better and engine technology in materials selection is miles ahead of our dads 58 Buick.

So why the short intervals in the book - at lot of that is worst case thinking. The OEM has no idea of the roll when it ships that chassis - RV, School bus, missile transport - who knows. Additionally- people are people, this thread proves it. 3K 5K 15K ask 10 people get 10 answers. Even if the book says 5K many go to 10 or 15K - because “I know a guy and he says….” Takes over from the OEM recommendation.

So your mission, your environment, your style of use has a big impact - but remember oil,is cheap - if you can outsmart the vehicle engineers - go for it.

Your mileage may very

[Midwestsurfguy]

Hello,
I thought I would post this informative video by an automotive engineer about changing your oil. This guy does a great job of explaining the science behind it.

https://youtu.be/eVyPWP5t09c

[ChicagoTom]

Thank you for posting this. I have a 2002 MR2 Spyder and I drive about 2000 miles a year. I was concerned with my once a year oil changes and often longer. No longer concerned. Great post!

Only one data point, but a pretty good one. (It was even sort of a blind analysis, since Blackstone had no idea how old the oil was). Reach your own conclusions. I have reached mine.

P.S. -- In case you are wondering, when we rescued the vehicle, I flipped my battery disconnect switch, turned the key, and drove off as if I had parked it the day before. So much for the "battery self-discharge in 3 months" theory.