juniormarbles

I asked this question on PCA's Tech page, but never got any replies:

It’s been claimed that Porsche owners should do an oil change at least once a year, even when the car is driven less than 5000 miles.

Oil is not particularly hygroscopic, and I cannot think of any other environmental or mechanical degradation that would make oil that was used gently for, let's say 1500 miles, any less safe for my engine's health than pouring ’fresh’ oil produced more than a year before use.

What is the scientific explanation for the ‘once-a-year’ oil change recommendation?

docdrs

If the oil is not used then there is no reason to change it. But if it has gone thru multiple heat cool cycles then there is degradation. Perhaps not in the ability of the oil to protect against wear during cycling, but thru time and related ph changes due to use, even though minimal. Then if the acidic byproducts are allowed to remain in contact with the bearings, cranks and journals for a prolonged non use time, premature breakdown may be possible. In a Nut Shell........change your oil and run it before you put your motor to sleep.........but what do i know?..... oil is cheap , motors are expensive

mike9186

I'm nice a year at a minimum or every 3-6k miles whichever comes first. I just got my latest oil report back from Blackstone and they said everything looked great and to shoot for 6k miles this time.

dgjks6

start here

http://www.spectrosci.com/resource-c...fation-in-oil/

Petza914

4,000 miles or once a year. I've done extensive Blackstone analyses including TAN & TBN readings of Mobil 1 5W-40, Motul 8100 xcess, and JGR DT40 at 5,000 mile, 4,500 mile, and 4,000 mile intervals and so far, the only one that doesn't show some degradation of the addative package is the DT40 at 4,000 miles, so with this specific lubricant, I may try to increase the interval to 4,500 miles, then back to 5,000 miles but with any of the others, I'd be doing 4,000 mile changes if I were still using them.

Macster

Oil gets contaminated from use. Combustion pressures force combustion gases past the rings and these gases contain water vapor and other compounds. These other compounds combine with the water in the oil to form acids.

The acids attack the seals/gaskets which can over time lead to failure of these.

While the oil contains additives to neutralize the acids a low miles per year car suggests a car that is not used in such a way to get the engine completely up to temperature and keep it there to boil out the water. The acidic level of the oil increases and the anti-acid additive package becomes depleted.

The only way to remove the acidic oil is to drain it and replace it with fresh oil.

This also removes the water that can accumulate in the oil.

This is a real problem. Even though I drove my new Boxster 4K miles in must a couple of months after buying it new an oil analysis found 7% water in the oil. The water content was high because even though I drove the car a lot it was in the dead of a KC Mo area winter and my observation (prompted by the amount of water in the oil) found the engine coolant temperature was often quite low even when driving at highway/freeway speeds. The engine just didn't get very hot and thus the water didn't boil out of the oil.

The problem with the water in the oil besides the formation of acids, is the oil becomes thinner. It is more prone to foaming and becoming vapor. The extra vapor can result in increased oil consumption as the AOS is inefficient at removing this vapor from the crankcase fumes as they flow through the AOS on the way to the engine intake manifold.

The increased foaming can result in aerated oil being ingested by the pump and supplied to the engine with ther risk of some engine parts experienced increased wear.

As with acidic oil the only way to remove the water and replenisht the anti-foaming additive package is to drain the oil and replace it with fresh oil.

sullivas

My extended warranty has a condition in it that says the oil has to be changed twice
yearly for the warranty to be valid. FWIW.

voiceprint1

any oil weight recommendations? (opens can of worms)

Cbst09

I diy my oil changes so I change it once a year on my Porsche which is about 3-4,000 miles. On the other cars in the house (acura mdx and Infiniti G35) I will go about 7,500 miles with synthetic oil.

Wayne Smith

Just to chime in, my DIY oil change is every 5000 miles which translates to every 75 days or so.

I've used Mobil One European Blend 0W40 (7.5 quarts) from Walmart with OEM filter kits. This has been over the last 2.5 years and 60K miles of my stewardship. Current mileage is reaching mid 90s.

Driving is a mix of freeway commute, long trips (500 plus miles), and spirited enjoyment. This is my go to car.

Over that time oil out and oil in have matched. I have done no fill ups in between changes.

2010 C4S. YMMV.

docdrs

As far as oil weight goes.....since most of the issues with motors is cold start up , then why would you not want a thinner, easier to move light weight oil such as a 0W multiviscosity ? Unless your initial start up temp is 90* all the time why wouldnt you use a 0W 40? This will give you greater protection than a 5W or 10W-30,40,or 50. If you want an example... just try draining the oil out of a cold engine vs a warm engine.....or trying to suck water vs honey thu a straw.

cosanchez

Well that going to open a can of worms for sure



basic answer is your trying to pick an oil that covers low temp start
​​​
​​​​​but also has the right properties when the engine is hot and the oil must retain its shear strength

996AE

Which warranty is that?

Or, my mistake, this was humor?

docdrs

I'm bored