Recommended Oil Change Interval
 

I normally don’t mention anything about oil change intervals, figuring that everyone can decide that for themselves. But, I’ve had a number of people contact me to ask what oil change interval they should use. So, I put together the following write-up, to address that question.
There is quite a wide variation when it comes to recommended oil change intervals for normal daily driven street vehicles. Vehicle owners get recommendations from:

• Quickie Oil Change places that usually call for 3,000 mile change intervals.

• Owner’s Manuals that now can often say 7,500 miles or more.

• Modern vehicle computerized dashboard oil change indicators that can vary anywhere from about 5,000 to 10,000 miles, depending on the model, brand and driving habits.

• Then there are the premium synthetic oils from mainstream Oil Companies and from Companies that only sell premium synthetic oils, who try to get you to buy their extra expensive motor oil, by saying you can use extra long oil change intervals, such as anywhere from 15,000 to 25,000 miles.

Trying to make sense of all those conflicting recommendations is enough to give some people a headache. So, let’s see if we can make some sense out of all this.

• You can completely ignore the 3,000 mile oil change interval called for by the Quickie Oil Change places. There is no technical reason to change oil that often in normal daily driven street vehicles. Of course it doesn’t hurt the engine if you do, but it is simply a waste of money and resources, while increasing environmental waste, with virtually no benefit to your engine. This recommended change interval is only so those Oil Change places can make more money off the unsuspecting motoring public.

• Owner’s Manuals have been known to drastically revise their recommended oil change intervals to far longer, at a model year change, even when nothing has changed on the model involved. This happens because Auto Makers can use longer oil change intervals to claim a reduced cost of ownership, while at the same time reducing environmental waste.

But, the reality is, it does not truly mean that the same vehicle as the previous year model, with the same oil, can now magically go perhaps an extra 50% or more between oil changes. These longer intervals are driven by Corporate Business decisions, not by Engineering decisions. It has gotten so ridiculous with some vehicles, that you are better off to ignore the overly long oil change intervals that are now commonly printed in Owner’s Manuals.

• It is fairly common for the computerized dashboard oil change indicators in modern vehicles to not match the vehicle’s own Owner’s Manual. Of course the Owner’s Manual numbers are an overall approximation of driving conditions and driving habits, where the computerized dashboard indicator takes into account engine temp, throttle opening, rpm, etc, etc. So, some people might assume that the computer is more precise than the Manual. But, don’t believe it, because the computer is programmed for extra long oil change intervals for the same reasons as the extra long oil change intervals printed in the Manuals.

I have a late model daily driver vehicle myself, with a computer oil change indicator that shows that I should go “TWICE” as long between oil changes, compared to my previous similar model from the same maker, which was only a few years older, all while they both were driven exactly the same. And of course the computer doesn’t know if I’m using cheapo discount conventional motor oil or very expensive premium synthetic oil, labeled as extended change interval motor oil. So, once again, you are better off to ignore the overly long oil change intervals that are now commonly indicated by the computer.

• Then we have the premium synthetic oils from mainstream Oil Companies, as well as from Oil Companies that only sell premium synthetic oils. And retail prices on those premium oils tend to be so high that their sales are weak in the marketplace. So, those Companies devised a Marketing strategy which advertises that their oils are so good that buyers can use far longer change intervals, such as anywhere from 15,000 to 25,000 miles. Their idea is, since customers can buy their oil less often, that it will offset the super high cost of the oil, in an attempt to convince the general public that the high price is justifiable. All in hopes of increasing sales and profits. But of course, Marketing/Advertising being what it is, they leave out the dirty little secret that, no matter how good any oil is, or how much it costs, it will still get extremely dirty and contaminated, thus needing changing, WAY, WAY BEFORE that many miles. More on that below.
Now we’ve seen that all the various recommendations above have only the interests of others in mind, rather than your best interest or your engine’s best interest in mind. Therefore, it is best not follow those oil change interval recommendations, if you really care about doing what’s best for your wallet and for your engine. So then, what oil change interval should we use?

I’ll answer that by telling you the oil change intervals I’ve used in normal daily driven street vehicles for years, why I do it, and why I recommend others do the same. Then you can decide for yourself.

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I use a 5,000 mile oil change interval in my own normal daily driven street vehicles. This interval is long enough that it lets you get your money’s worth from the cost of the oil change without causing any negative impact to an engine. Changing oil much sooner than that, obviously does not hurt engine, but you’d be throwing money away for no reason, since shorter intervals provide no benefit to an engine.
I've sent a number of quality used oils with 5,000 miles on them, to a motor oil Lab for component quantity testing, to see how much the additive package components had been depleted during that interval.

Here’s what I found, on average, for that group of oils:

• The overall anti-wear package component levels had dropped by about 24%

• The detergent level dropped by about 9%

• And the TBN (acid neutralizer) dropped by a significant 51%

The reason so much of the additive package was still available in the used oils I had tested, was because those oils were subjected to only normal daily driving. And additive package component quantities are typically high enough to begin with, so that they won't be totally depleted prematurely by severe/extreme usage, such as racing, heavy loading, towing, mountainous or off/road operation, extended idling, or extended hot or cold operation, that could take place, where the additive package would be used up at a faster pace.

I also “wear tested” those used oils myself, and found that there was no loss of wear protection, even though the zinc/phos (ZDDP) level in particular, had dropped by about 25%. And that is clear proof that ZDDP levels DO NOT determine wear protection capability.
Additive package component quantity depletion, as mileage accumulates on the oil, is normal. The various components are used up as they do their job. And after 5,000 miles of normal daily driving, there was still plenty of additive package remaining in the oils tested above. BUT, that absolutely does NOT mean that you should keep using motor oil until those components are completely exhausted. Here's why.

One of the primary reasons your oil gets dirty, is because of combustion by-products getting past the rings from blow-by, and entering the crankcase into your oil. And this has nothing to do with how high tech the engine may be, or how good or how expensive an oil might be. This happens to ALL motor oils in all engines. And oil filters CANNOT filter out this contamination from the oil, no matter how good some filters may be. Because oil filters only filter out particulate matter. Filthy contaminated dirty oil will flow right through any oil filter. So, continuing to run filthy dirty contaminated oil in your engine, would be like using the same filthy dirty contaminated bath water for months, and months, and months. You could physically do that, but you would never be clean. The same thing applies to your engine.

In addition to this, small amounts of fuel also get past the rings, particularly during cold start-up and during initial warm-up, when the engine is running extra rich with fuel. This fuel slowly dilutes your oil, again no matter how good the oil is, or how much it costs. So, this is another important reason to use reasonable oil change intervals, rather than extended change intervals.

And if filthy dirty contaminated diluted oil isn't a good enough reason to avoid using extended oil change intervals, consider the following. Every motor oil is different, so it would be very difficult to establish a general oil change guideline to use, to get closer to the limit of total component quantity depletion, that would be safe to use for every motor oil, without going too long on certain oils and run the risk of totally depleting those critical additives. And if an oil is subjected to severe/extreme usage, then it makes this issue even worse.

And to further complicate things, even motor oils that are marketed as extended change interval motor oils, don't all follow the same plan for the amount of extra additive package quantity put in an oil, which might allow you to even consider going longer. If you look at " Section 4 – Motor Oil component quantity Lab Test results", in my Blog, you will see that some name brand motor oils have extra additive package component quantities in their oils marketed as extended drain interval oils. But, other name brand oils marketed as extended drain interval oils, only have normal change interval additive package component quantities. And the normal change interval oils they sell, actually have below average quantities of additive package components.

So, the only way you could ever safely consider running motor oils longer than reasonable (if you don't care enough about your engine to consider the filthy dirty contaminated diluted oil aspect), whether the oils are marketed as extended change interval oils or not, is to take a small sample of the oil being used, and send it into a motor oil Lab for component quantity testing every few thousand miles, after you've reached a normal change interval mileage. That way you could make sure you don't ever run completely out of critical additive package components. But, of course that is simply way too much trouble for most people to ever bother with.

And if all that isn't bad enough, remember that motor oil deteriorates any time it reaches its onset of thermal breakdown point. And that thermal breakdown point varies widely from oil to oil, with many oils reaching that point as low as 250*F. Oil temps are not the same everywhere inside a running engine. Typical main bearing oil temps can be 55*-90*F higher than sump temps. So, oil temp gauges installed in an oil pan can give a false sense of what max oil temps actually are inside an engine. And with extended oil change intervals, you need to consider that most oils have also been deteriorating from exposure to temps that exceed its thermal breakdown point. Therefore, every technical aspect is negative, regarding extended oil change intervals. Meaning that there is absolutely NO technical benefit what so ever, to using extended oil change intervals.

BOTTOM LINE: By the time a normal daily driven street vehicle reaches 5,000 miles on its oil, that oil is dark dirty contaminated, becoming more and more diluted as time goes on, and has been suffering some thermal breakdown deterioration, so it is in definite need of changing. People who go much longer than a 5,000 mile oil change interval, just don't understand the technical reasons why that is NOT a good idea, even if they use very expensive premium synthetic oils marketed as extended change interval oil. But, now they know, so they can make a more informed decision about the oil change interval that is best for their engine.

CONCLUSION / RECOMMENDATION:

• I use 5,000 mile oil change intervals for conventional or synthetic oils, in my own normal daily driven street vehicles, for all the reasons discussed above. And it works out that it is also convenient to see when an oil change is due, by simply looking for 5,000 mile increments on the odometer.

• I would NOT use shorter change intervals for normal daily driven street vehicles. But, I would and do, use shorter change intervals for vehicles that are subjected to severe/extreme usage.

• I would NOT use longer change intervals, not even with premium synthetic oils labeled for extended change intervals, for all the reasons discussed above.

• I recommend using the oil change interval I follow, for those who want to provide their engines with the best protection.

For the truth about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 150,000 views worldwide. You can see the Blog and my entire 170+ motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Credentials, methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.

http://540ratblog.wordpress.com/

540 RAT

Wow that's a lot of info for a simple answer....
Mobil 1 and when my DIC says 15% I change it ... or at least once a year...

Ive stuck to my 3k interval on all my cars synthetic or not. They get driven hard and its cheap piece of mind.

Too complicated.

On a street car, once a year or 7500 miles is what I go by.

Before it was every 6 months regardless of miles but I haven't been driving much now given work is close to home.

On my GS, I only did 4k miles but in 13 months. Gonna change oil as soon as spring comes.

Same unless I take to the track, then I change more often, but as I get older, I don't go much anymore. I use Red Line oil.

I must be the exception here, because I have changed my oil in all my vehicles at the same intervals as the OP recommends , 5,000 miles, and never had a oil related problem with any of my cars...:thumbs:...WW
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I don't think you will find anyone here that has had an oil related problem after following the DIC OLM either which can be far beyond 5,000 miles in a year. I don't drive mine 5k miles in a year so I change oil once a year and sometimes a little longer.

Dashboard nanny or 1/year, whichever comes first.
There. fixed it for you :)

Excellent information - thank you for posting it with technical data (link) to back it up, clear and concise -

There will be differing opinions but I do appreciate the information and is pretty much spot on with what I do with my vehicles! :thumbs:

IMHO - I do like Mobil1

Thanks,Matt

That info might fly on the average non-performance car forums, but when you posted on the C6 forum, it's a whole different matter.

We all have a sophisticated system that has no relationship to miles. It's not some gimmick promoted for car sales or early changes. The owner's manual spells out the basics of how the system works and the fail-safe is programmed at half the total depletion of the recommended oil life span.

According to your 5,000 mile change, there is no method to indicate if there is a need to change earlier or a reason that it can be extended a lot farther. With the OLM, it measures the reasons oil is depleted and presents them in a % method that is easily understood. The OLM would indicate the time to change oil, even if the car had no miles, such as only idling in place, simply because the engine is running. The OLM would also indicate time for a change, if the trips were only 1 mile each, because the oil temps never were at normal. It'd also indicate a change due to high engine speed use in relation to car speed, such as stop 'n go rush hour traffic in lower gears or at a competition event like drag racing etc.

The converse is also true, that on long road trips where the engine is loafing at 1300 RPM at a steady 60 MPH, the distance traveled in one minute has the same engine revolutions as two minutes at an idle with zero distance added.

Now cars makers have long indicated the time or distance they approve. Most consider a 1 year period is the maximum. The reasoning behind a year, is that when you don't pay attention to things like miles, you have a better tendency to remember events on an annual basis. Birthdays, anniversaries, deaths, jobs, and major purchases all relate to annual events and therefore, so can oil changes for forgetful people. Annual oil changes have been ingrained in the public's eye, just like the 3,000 mile changes of the 1950's.

The bottom line for C6 owner's is to follow the OLM and dis-regard all other methods. You'll never have an oil related failure if you change oil while the OLM still has a number. It changes to CHANGE OIL SOON at 3%. GM didn't spend untold millions in research to create a system to fool you into a false sense of security. If you can't trust the OLM, then there's a lot more electronics in your daily life that must drive you absolutely crazy. :D

The other comments about filthy dirty oil, such as "oil filters only filter out particulate matter. Filthy contaminated dirty oil will flow right through any oil filter." are mis-leading at best. The reality is that oil filters remove particles that are larger than the largest opening in the media. It's no different than any other type of filter, since the object is to allow particles of a smaller size to pass through. Particles of dust/dirt that are smaller than the openings will always pass through and therefore allow oil to appear dirty. The color of used oil is not an indication that the oil is bad or needs changed.

I would like to thank 540RAT for his post on 01-13-2016 regarding oil change intervals. It is seldom that one finds such documentation derived from empirical data regarding any topic much less oil change intervals many of us take as a personal matter just because we have being doing it the same way forever. Thanks both for the effort you expended in gathering this info and for your willingness to share it with like-minded members of this forum. Sharing ideas and bantering back and forth with topics ranging from silliness to the sublime is part of the fun of any forum. You and other members who submit such posts based upon actual research goes beyond what many of us can do and is what makes these forums so valuable to all members. Any detraction and/or disagreements are an important function as well by adding additional aspects of any topic to be considered and discussed by members. What would any forum be without them? I was lucky to have viewed this C6 section as I spend most of time On the C7 section. Hopefully this will explain my delay in responding to a very interesting topic.
Thanks again and Be Well,
Ralph

:iagree: <5% OLM or one year whichever comes first. GM has already programmed conservatism in the OLM programming so 0% is not really 0%. Plus use full synthetic oil and your car will never have an oil related problem. JMHO Your results may vary.

it would seem he can't decide for himself.

Ditto, plus this on "filthy contaminated dirty oil will flow right through any oil filter." The color of used oil tells us almost nothing about its suitability for further use. It is a demonstration of a number of factors; only one of them is dirt. The filter fineness is calculated to remove particles from the oil that are larger than the oil film in the engine is thick. Particles smaller than that film is thick will discolor the oil but will not damage the engine.

For a lot of years I submitted for analysis oil (always Mobil One but once, when it was Kendall racing oil) from every second change in my BMW and Harley motorcycles; we're talking about a cumulative 300,00 miles. Except for the Kendall (which had no detergents,) in every case oil submitted at 6k miles was reported back as being "Suitable for further use." In one case, BMW oil submitted at 8k miles was still suitable, but a change by 9k was recommended. I did so. Based on those reports I usually changed my oil at 7,000 miles in either bike, but even then, if I was on the road and no more than a thousand miles from home, I rode it on in and did the change.

Since those air-cooled engines were much harder on oil than a water-cooled V8 I have no qualms about running my interval out to whatever the OLM reflects.

For in-depth oil information provided by a petroleum engineer, drop by Bob Is the Oil Guy site at http://goo.gl/j7zWWE

Pilgrim

:iagree:

My 07 DD has over 210K miles on it and runs great! :steering:

Think of how peaceful your mind would be if you changed oil every 1,500 miles. :rofl:

Pilgrim

That is not a bad idea.........:D

I change oil at one year or 10,000 miles.

Whenever you change the oil in your Chevy, or do any other service or repair, be sure to log it here... I think not many owners are aware of this tool:

https://my.chevrolet.com/web/portal/managemybrand?g=1

Personally I follow the owner's manual: 7500 miles -or- 1 year -or- when the "change oil" light comes on, whichever comes first. I use the recommended Mobil 1 5w30 and high quality filters. And maybe I'm in a lowly C4 but the OP didn't discuss cars, just OCI :)

Thanks for the info! :thumbs: