Oil Change Intervals - Science

Porsche recommend 12,000 mile oil change intervals for 986 Boxster and 20,000 mile (or every 2 year) oil change intervals on 2005-2007 Boxster/Cayman / 911 , but lowered that recommendation to 12,000 miles (or every year) for just MY2008. When Porsche 's new DI engine came out in 2009, they lowered the recommended oil change interval to 10,000 miles (or every year). The reduction in 2009 is understandable as the DI engine operates at higher pressures and would get more ring blow-by. Commercial fleet vehicles in Europe have oil change intervals of 60,000 miles or more. However, a number of people here still change their oil at the same 3-5k miles, and love to post about it. There doesn't seem to be much fact or reason thrown around when people choose intervals, just a lot of conjecture, superstition, and conspiracy theories. I'm an engineer and a scientist. I like facts, and I like to keep my car running well. I like to base my maintenance practices on facts and data and created this thread so that we can discuss the facts and data around oil change intervals. One fact we know is that Porsche recommends oil change intervals in the 10-20k mile range for their water cooled engines with full synthetic oils. I know the oil samples I had for my hard-driven 986S indicated 11-12k miles were the right interval. To start off the discussion, I pulled some recent literature on the topic to see what scientific studies had to say about oil age and wear: * A landmark 1974 study found oil change intervals could be doubled with the switch from leaded to unleaded fuels with no significant difference in deposits or wear. There were some other adverse effects that were negated by different concentrations in additives (Loren, 1974). * A 1996 study designed to help guide motorists in the right oil change interval (like we're talking about here) found no clear correlation between oil change intervals and wear metals and additive related elements (Springer, 1996). Thus, it may be that other variables Springer didn't test have far more impact on oil life than simply time or miles. * Extremely-long-life oils (100k+) exist, but technological gains are hurt by emissions requirements such as exhaust gas re-circulation, retarded timing, and higher bore pressures (Margoni, 1999). We're reaping these benefits with extremely long life fluids in applications not exposed to these contaminants, like transmission oil. * A 2007 Ford study found 12,000 mile old oil actually lubricated better than fresh oil; it had 10-15% lower friction and an order of magnitude lower wear rates. They found samples changed at 3,000 miles and 12,000 miles had very similar compositions of tribochemical lubrication films (Gangopadhay et al, 2007). I unfortunately can't find the full paper; I'd really like to see more detail on this because it's completely counter-intuitive. I've heard this mentioned before in various oil threads, but this is the first time I've found an actual study about it. * A Texas DOT study two years ago found there's very low oil degradation levels associated with low load conditions, and that fleet oil change intervals could be significantly extended in some vehicles based upon use (Ramani et al, 2015). Lots of highway cruising is easy on the engine AND on the oil, it seems. I know a lot of us do oil analysis, what have you all found on your Porsches? Anyone else have any good scientific studies or papers on this subject? edit: make sure to post what your car is if you're talking about oil analysis/change intervals so we can compare apples:apples

Blackstone has some good articles on their website, although they are not rigorous scientific papers. I sent them a sample with 6,800 miles (48,000 total miles on car). All measurements came back within the normal range. TBN was 5.8 and they recommended extending the change interval. Some years I drive very few miles and I asked them about the time interval - their response was they have not seen much issue with time; the person responding said she had just analyzed a sample that had been in a car for 10 years and the results looked fine.

Not the reply you are looking for, I know. No statistics or science. If Porsche changed from 20k in '05 to 12k in '08 they had to have a reason. Probably failures that happened under warranty. I have no warranty. Changes at 5k are cheap insurance for me.

They didn't reduce the recommendations for 05-07 cars, though, they're still recommending 20k intervals. Only 08 is different. I'm not sure what changed.

from my post 6 months ago: what do you think about it? They said that oil was close to new and suggested to prolong oil change interval.

Isnt 2008 the last revision of the IMS ? Maybe that new IMS bearing had different needs.

What seems to be missing in this conversation is how the car is used. i.e. I would have assumed that fleet oil changes could be pushed out because I assume that the cars are driven long enough to fully heat up the oil. However, consider the user who uses the car as a DD to and from work, as I did, and work is 2 miles from my home. Oil never gets up to temperature so water is never boiled off. Synthetic oil helps, but does not eliminate the formation of acids and other undesirable chemicals in the oil over time. If you read the 981 Boxster SIT you see that Porsche goes to great lengths to heat up the oil as fast as possible. This is done primarily for efficiency purposes but also helps in the short drive scenareo. Porsche , just like your 3rd grad teacher, has to target the lowest performing individual. Or in this case the DD who never lets his car fully warm up. That my explain why there has been fluctuation over time on the recommended milage per oil change. I've noticed that the one year interval seems universal across makes at least that is true for my Honda S2K, MB ML320, and Audi S4. All of which have very different milage recommendation for oil change.

I think I'd go with the expert recommendation, but this is another area where UOA interpretation seems to align more with technician opinion than any actual science. The deeper the go in the rabbit hole, the more I find that somebody's best-guess judgement call made with zero evidence besides a gut feeling gets taken as gospel and in some cases literally gets codified.

I drive 4 mile trips several times per week. Feels like abuse so I try to get some heat in the motor at least 1 or 2 times a week. Thats the main reason I change oil sooner than most.

I would love to hear more science on time based oil changes. My '11 Boxster is a pleasure car and only get's driven 3-4k per year. Even though I don't drive a lot of miles it would be very rare for me to drive the car and not get it up to temperature. "I asked them about the time interval - their response was they have not seen much issue with time; the person responding said she had just analyzed a sample that had been in a car for 10 years and the results looked fine." This seems to indicate that changing based on time isn't important but as another member said every manufacturer seems to have a one year interval. Is this to preserve service income or is it based on a scientific reason?

Very interesting thread. I think it's safer to get oil changes done when the motor is brand new at relatively low miles because of the metal filings that get produced. As the motor matures I think it's fine to match the recommended intervals. I reckon I will be doing 5k miles a year on my Spyder so I am a bit torn whether I should do the yearly oil change or not. Let's see how it goes. If I track the car 3 times a year then definitely oil change is taking place because of the stress. If not then I would wait.

Another possibility is that manufacturers have to put down a number that balances buyer expectations and their ability to void warranty coverage. After the warranty period is over, the manufacturer is unlikely to care what interval is used.

That is what the oil filter is for. Modern engines have such high tolerances that there are little to no metal filings visible in the first oil change (filter) like old timers used to see . I hammered my car out of the gate. Not kidding - 400 miles on the car and I was driving it hard into the 6000 rpm range up steep slopes in the swiss alps. Oil temp (in sport + mode) got up to 246 degrees. 10k miles later I got the oil change done. I took the filter home and dissected it. I could not find a single metal filing. 31k miles later and four bars as usual on the MFD. No oil usage. I think the oil change interval recommendation is based on worse case scenario and is very conservative. Age related degredation is not as much of an issue with synthetics. Water and contaminant build up perhaps but modern engines have much less of that problem.

I work professionally with a lot of big engines, some of which have hundreds of gallons of lubricating oil. Needless to say, we use UOA extensively, and often go many years between changes in some applications. Modern synthetics last a long time. I suspect Porsche 's "1 year" thing is a catch-all to cover people that do lots of short trips that don't build up enough temp to drive off moisture more than any actual age related degradation. But, I don't want to speculate and we don't really have any data besides we know it's what Porsche specified.

A couple of years ago in a ******** discussion, you brought forward the idea that its really moisture that destroys the race bearings in the IMS . So for those of us with an IMS , I would think it prudent to change oil around that issue not what the oil analysis says. Unfortunately we cannot assay the grease inside that bearing as you know from your 2004 Boxter, but when it was changed, it was like new, so what ever oil change and drivers style you have worked well. My 2007 Cayman S IMS is not a candidate for repair or replacement, only when I have my clutch replaced, I will have the seal opened to engine oil, but before that time, I am running 5W-50 Castrol with ZDDP and changing at 5000 or less depending on how much track time is done. I also am trying to warm up the oil as fast as possible to get the mosisture out of the oil. I wished I had science on my side on this one as well as I live in Seattle where it rains a lot, meaning high moisture levels.

I used Blackstone for my Lexus is350 at 5k miles, and 50k on the car. They suggested extending out to 7.5k and testing again. I just got my Boxster s 981 , but intend to do an oil change around the 8k mark and have it tested. Seems testing is the only real way to know what condition the oil is in. Maybe a few people here that drive "hard" could spring for a test on their next oil change? Depending on who does your oil change, the cost of the test may more than be made up for by the extended oil change made possible. Also an engineer, so I'm all about testing and facts as well. Gut feelings scare me a little Matt

Since I do a lot of short trips and put fewer than 3k miles a year on my Cayman, I think moisture may be more of an issue for me. The one Blackstone test I did showed 0.0% water, but I'm not sure how indicative of average moisture level that is. They stated you should drive your car for 20 minutes before taking the sample, which I did, so presumably a 20 minute drive is sufficient?

I like to think that Blackstone report will magically protect my engine and IMS , but, but the moisture level is illusive and their report rarely shows much as I have looked a various reports from this web site and others. So for me its black magic as I change my own oil, carefully letting as much as possilble drip out of the oil pan, before replacing the magnetic drain plug . The current oil change is about $100 for 8 quarts of Castrol 5W-50 and an oil filter. About $200/year insurance for me with about 10,000 miles per year. My cam chains are also notibly less noisy with this oil. Not sure about how long it takes to remove the moisture from it every day, but usually my drives are at least 20 minutes and some spirited driving at the end of that time to get the grease in the IMS bearing heated up (not covered by Blackstone's report). Thinking about adding oil temp and pressure gauges that sort of match my dashboard face to help put some science into what I am doing daily and also help at the track.

Science and objectivity means taking into account the volume of oil in the flat 6 engines. It is roughly double that in some other engines, along with the amount of additives in the oil. This should be taken into account when considering studies done with other engines.

My 981 has an oil temperature gauge and I noticed today that it took 18 minutes of freeway driving in the low 80's to reach 212. In city driving in cooler temperatures I have seen it take as long as 30 minutes.

Pretty much the lower the interval the more often the dealer can see your car. That's what I think. If they can check your car out more often they can see other things to "fix" for you. Sent from my iPhone using Tapatalk

" Not sure about how long it takes to remove the moisture from it every day, but usually my drives are at least 20 minutes and some spirited driving at the end of that time to get the grease in the IMS bearing heated up " Until we can determine the exact rate of moisture creation as well as the rate of moisture dissipation, and at what variables, all we're doing is guessing about short trips and how it may damage the engine.

I've been a member of various car forums over the years. Oil/OCI/Filtration/Analysis is a topic much more shrouded in religion than science. I used to work for a bearing manufacturer as a design engineer, and there are resources out there - but opening a discussion on an auto forum is not likely to result in more than a bunch of personal, anecdotal discussion. https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=cfrm is probably the best place to go for a public discussion. It looks like you've already started out on a more objective search - certainly the best keyword is Tribology, as you already know... There are stories of people who use very sophisticated filtration systems on big rigs, and do nothing more than refresh additive packages - but for people like us, be it needed or not, a 5,000 mile or yearly change in something as expensive as a porsche seems to be a practical (if overkill) approach. (Mine is not a DD - if it were, perhaps I'd consider a slightly extended interval) - but that also is just a personal, anecdote...

What type of code reader to you have that will reset the service reminder. Mine is set at 10,000 miles and I have changed the oil 3 times since I purchased 07 CS with 23,000 miles on it. I would like to use somesort of reader to reset it rather than an indy. Thanks, Ken

There are several threads on the topic. Personally I'm a fan of Durametric because of all the additional diagnostic/maintenance things it allows you to do. Many people are put off by the $300 price for the Enthusiast version, but if you buy/sell on Ebay, your net cost is $100/VIN. I bought mine for around $200 with 2 VINs left and will sell it for around $100 on the sad day I get rid of my Cayman .

A few interesting scientific studies about oil that actually indicate that fresh oil has considerably worse wear characteristics than used oil: https://www.sae.org/publications/technical-papers/content/2007-01-4133/ (This is the Ford study cited above) https://www.sae.org/publications/technical-papers/content/2006-01-1099/ https://www.sciencedirect.com/science/article/abs/pii/004316489390294V The question is where is the fall-off in performance. At what point does a specific oil lose it's anti-wear properties with use?

I agree we could extend our daily drivers, except that I have a 07 Cayman that still has a IMS bearing . Engine oil could penetrate the IMS seal over time, so the prudent idea is to change the oil with that issue in mind. For track cars, oil that has been exposed to thermal breakdown, like on long runs on hot days with only standard radiators and a standard sump, engine oil could become cooked, losing a lot of wear protection, film strength and load carring capacity.

wow! a few possibilities: 1- going a little long between changes might not be as bad as one thinks 2- changing less than all the oil (say 50% or so) might be a good idea for those who want to change the oil frequently (like every 3-5000 miles) 3- those quick lube places might be doing people a favor when they don't drain out all the used oil 4- changing my own oil and thinking that I drain out more used oil (because time is on my side) might not be as good as I thought

If you have a 09 or later Cayman and you do not coke your oil with high temps on the race track, the only down side is oil receipts if you want to sell your car. Most average Porsche people are ardent maintance followers. Not only changing the oil but what about regular maintance of other fluids, brake fluid, transmission fluid, toping the coolant, general maintance car cleaning, interior leather cleaning. Just knowing that the oil was changed every 6000 miles would be a turn off except if a workbook could back up these oil change intervals. Not sure that viscosity is a key oil longevity reference point as it does not determine an oils wear protection capability as referenced from RAT/540 blog.

The factory fill in all current-model Porsche 's (except for the upcoming Taycan !) is Mobil 1 0W40. Honestly, I'm not sure what conditions warrant a change in viscosity. I would love to see some definitive recommendation on that from Porsche . Seems like generally they recommend 0W40, but 5W40 and 5W50 is also an allowable viscosity per the owner's manual for temps above -13F.

If Mobil 1 0W-40 is used, specify FS label. Much more wear protection capability.

I did not see the measurement of sediment in the engine. Just because old oil does a good job of lubrication that does not tell me that sludge is not building up. I will keep changing at 5k intervals.

I believe the old non-FS version has been retired, but at least per the 540Rat testing, the new FS formulation appears to be miles ahead of the old version. I also do Blackstone testing on all my oil changes. The Blackstone reports along with the information I've been reading about oil life, is helping to ease my concern. I did post a question on the 540Rat blog about his recommended oil change interval. Although he claims to be all about the science, this is the only place where he uses purely anecdotal evidence and refuses to acknowledge any science that backs up longer oil change intervals. He would not acknowledge that he was refusing to accept the science, and didn't seem interested in doing any testing that might sway his recommendation. He was pretty stubborn about it. I've always been a 5K mile oil change guy, but the science is leaning toward 10K+ oil changes not really being a problem with modern synthetic oil. I beat up the oil pretty hard, daily driving in Texas summers, plus averaging about 6 track days and ~10K between oil changes. The Mobil 1 0W40 FS oil has held up well, with some shearing down of the viscosity due to high oil temps on the track, but even with >9000 miles the wear indicators and oil life (TBN) look to be in really good shape. The 6700 mile oil change was right after I did a 3-day DE at COTA and my oil temps were hitting 275F @ 104F ambient. I wanted to be a little more cautious after that 3-day beating in high temps, but based on the numbers, I think 10K would not have been a problem, even after that beating. I'd like to not have as much shearing, so I'm going to be putting a 3rd radiator in to try to bring down my oil temps at the track. That said, I read in a Porsche Panorama article that the 981 GT4 Cup can run oil temps in excess of 290F @ 72F ambient without concern about lubrication issues. Attached is my latest Blackstone report. My first oil change was from PZ Ultra Synthetic 5W40 (which has a slightly higher viscosity) to Mobil1 0W40. The oil was changed by the previous owner at Porsche of Nashville right before I purchased the car. Interesting they didn't use Mobil 1 . Blackstone noted the "Unit/Location Averages" wear levels are based on the same Porsche 3.4L NA engine with a 4100 mile average oil change interval. So my numbers at 9600+ oil change intervals are better ppm-introduced-per-mile than a 4100 mile interval.

If you have sludge build up, you would see increase in insoluables and/or an increase in viscosity in the Blackstone report.

Still sticking with 5k. Clean oil makes me feel warm and fuzzy. I cant remember anybody saying "My motor locked up because the oil was too clean".