Why is it necessary to change oil after one year regardless of low mileage?

I understand our oil has cooling powers, lubricates the engine and pushes foreign materials to the filter. Oil does not "break down" for tens of thousands of miles regardless of summer vs. winter operating temperatures. Does it go stale like milk? What difference does it make if it exceeds one year old? I run more than 10k miles a year so this is really not relevant to me. I'm sticking with the 5k mile changes to represent to a future seller that I perform frequent maintenance; but, in realtity shouldn't oil be changed because it gets dirty and not because it goes bad or breaks down?

I believe that moisture in the oil is the enemy, which can corrode internal engine components.

Corrosive wear and high total acid numbers in oil are often not considered. Time and experience has taught us that a 6 month/ 5K mile service interval is what these engines like. If you listen to the engine you'll never go wrong, because it doesn't know how to lie.

I'm not a "Porsche- Whisperer", but I'd guess the special additives blended in the oil would have a suspension issue if left "un-stirred" via use. Motor oil is only a few processing steps beyond that of diesel fuel. Diesel fuel becomes extraordinarily unstable if left static for any extended period of time. Moisture, algae, and general funk of de-homogenizing ruin the fuel and wreck the fuel tanks of diesel systems. Ask any diesel boat guy how old fuel affects their boat... I'd guess some similar badness happens with stale oil over time.

But wouldn't they then degrade on the store shelves?

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Not in a sealed HDPE/PET bottle, and the rate at which it is sold in high volume retail stores.

Some very good comments in this thread . From years of flying with & rebuilding Rotax motors , it is commonly accepted & been documented that synthetic lubricants are moisture producers when left for any period of time in a dormant motor . Yes, I'm referring to 2 stroke motors , but this has also been documented relative to 4 stroke as well . With the current use of synthetic oil being used today in everything, I have to believe this moisture problem has somehow been curbed by the oil chemists but to what extent , who knows ? In my 01 C4 manual it mentions using a syn blend (syn & natural oil) as an acceptable oil , which I may do rather than a full syn, or maybe straight non syn as offered by Castrol , my oil of choice for many yrs except for Rotax 2 strokes , whereby a natural oil based mix is used by most everyone for best lubricity , worry free storage , & low carbon buildup . So, should you chg your syn oil after an extended dormant period--definitely, as verified by the excellent comments mentioned by Jake , Dennis , & TS Mc Neil . I run non syn in my street rods & do not worry about moisture, storage, or lubricity ---if the oil stays clean--I drive it , up to 3-4 k , then chg . Bob 01 C4 31 Ford cp chp & ch, 302/350 40 ******, 302/350, IFS 38 Ford cp, 327/350, IFS 57 Belair 62 356B --long ago

If you are doing an annual oil change and storing the car for the winter 4-6 months, do you change the oil before you put it away or as soon as you put it back in service? Coming over from Corvettes and we always changed the oil in the fall before storage, assuming the same with the 996.

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Just to confirm: Oil changes should be done twice a year at a minimum regardless of the mileage. Correct? I've been changing the oil every 5k miles which is usually just once a year.

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You feel like rebuilding my Rotax out of my Aprilia RSV1000? I think it has a couple bent valves.

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alpine003, how in the world? When I twist up my Aprilia it goes so damn fast, I gotta back out of it!

It doesn't matter the make/model of car...oil is oil and it wears out. Change it twice a year, spring before it gets hot and fall before the dregs of winter hit, if it's a daily driver. It is such a small price to pay when you're gambling with a very expensive motor. Use a Porsche recommended total synthetic oil. I run M1. Been doing this for 50 years on every car I've owned. It just feels right to have fresh oil in the car, and doing an oil change just makes you feel good. 99 C2 996/911 DD w/130,000 miles. As the commercial goes...just DO IT!

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Change the oil/filter before putting the car away for the season. This removes the old oil with its acids and the engine spends its idle time with the least corrosive oil in it.

Synthetic oil doesn't wear out. What happens is it gets contaminated with mainly water and other combustion byproducts. Water lowers the oil's viscosity to the point its ability to provide high temperature high stress oil film protection can be compromised. Additionally the water and other contaminates combine form acids, and these attack everything the oil comes in contact with. Draining the oil removes all the water and acids and the fresh oil brings with it a full strength additive package and the process starts all over again.

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Err who told you that nonsense to begin with? The air inside the crank case is a sealed system, so whether you run it 5K miles in 1 year or two years won't make any diff vis a vis air moisture etc.

Gotta love oil threads..........again......

I intend to switch to this oil starting with the next oil change. What you guys think?

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I really don't know as my motor blew with 2k miles on it. I suspect the previous owner over revved it and/or didn't break it in correctly. I wasn't happy to say the least. Got a used motor replacement but still hung onto my original motor. Love the midrange v twin torque. Great for wheelies.

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This is nothing for an oil thread...I've seen them go for years on the ///M forums. lol

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TWS!!

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Yeah, mine's on it's second motor as well from track day foolishness via the PO, I do like that hit starting around 4,500rpm! Oh yeah, oil, what Jake says....

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I believe there may be a vent back to the gas tank or intake manifold. Have trouble believing crankcase is perfectly sealed. The volume of air in there with the hot vs cold temperature range would cause a pretty good pressure build up. 2002 Turbo - Basalt Black Metallic / 2003 Carrera 4S - Speed Yellow / 1955 356 Continental 1500 - Rust Red

The AOS bleeds crankcase pressure back to the intake manifolds. Now back to the OP's original question - why do I have to change the oil? For that matter, why change the oil filter, air filter, tires, brake pads, brake fluid, pollen filter, or add air to the tires??.... It's a Porsche and that stuff will last forever. It's your car and you can do whatever you want. I keep mine exactly the way it left the factory and never change anything. Those car engineers/manufacturers have no idea what they are doing, and c'mon, they are really just creating circumstances where you have to go back to the dealer for service so you'll lust after all the new models and end up buying one. The heck with that...rebel and don't fall it! Make a new revolution and never, ever follow anyone's advice, especially a bunch of Porsche engineers, or Jake even.

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Best comeback I've read so far anywhere in this forum --in fact I wanted to comment on the "sealed crankcase" (ha) but I couldn't have done it this well ! Maybe that's where the comment came from all those years in engineering relative to user/product interface-- " design it so it's idiot proof "

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I agree with you.... however, as an engineer myself, I know that many of these recommendations are based on covering the extreme cases. For example, non-synthetic oil is more prone to breakdown and MUST be changed over a given time period. Most pure synthetic oils are much more stable, and the time isn't a big issue. Some synthetic oils may be blended with non-synthetic. So the engineer recommendation to change the oil every year is based on these extremes. If you want to know the truth, just analyze your oil over time based on your current driving habits etc, and you should be able to tell when you need to change the oil..... or just follow the recommended procedure and feel confident that you are covered. BTW - Porsche engineers recommend changing oil every 15k miles, so lets not just assume that this is "what's best for the car" The recommendation was probably based on a replacement timeframe of 7 years or so, and not meant for 15 year old cars.

Trust that the health of the engine isn't the only consideration in these service intervals. When buyers look at the cost of ownership they don't want to see that 3-4 services are required per year at 3-400 bucks a pop. Even though this is really the case, they still don't want to see it. The same for leasing companies, I am blown away at how many broken cars that we buy that were originally owned by a leasing company. The leasing companies won't fill their fleets with cars that require a ton of service as they are responsible for it.Its no coincidence that the cars that seem to break so often were originally a leased vehicle, because they only got the service that the factory called for, nothing more. And, I don't care if the oil will last a year, when I change my oil I want to purge impurities from the oil sump that are there from the combustion processes. Whether the oil is good or not, it is laced with impurities. These engines are even worse as they are notorious for fuel intrusion that stems from a lack of ring seal and over enriched starts cycles that are meant to light off catalytic converters faster. Its the things that you don't know that always worry me.. Thats why I work to learn as much as I can, never stopping and never giving up.

I am the original OP and was not advocating not doing an annual change......just curious why. There's really good data on this thread.