Value of oil sample question
 

I aend oil sanples oit to blackstone at each oil change for my 993 and my Cayenne. Blackstone says there is plenty of additive left in the oil on my Cayenne at 7,500 mile intervals and they suggested going to 10k miles. I know very little abou oil analysis so, aside from addotives remaining, how would I determine the safety of going for 10k oil changes?

You can find on the web any number of papers/etc. The answer is probably "it depends".
IMHO and given the input from Blackstone - I'd say 10k is fine. There is also the argument that sooner is better - oil is cheap, Porsche engine rebuilding is not.

If it's not full of gas, out of range viscosity-wise, still has some base number left, and your wear-metals aren't thru the roof it will be fine. Considering that our oil capacity is ~3x what you see in a normal car it's not at all unreasonable to expect long drain intervals.

I run Rotella T6 in my 964 and have multiple samples at 15k intervals showing no cause for concern.

Total Base Number is probably what they're referring to. Compare the TBN from new oil to the TBN measurement from Blackstone, and you'll see how much life you have left. I'm not sure what a safe limit would be, but you probably don't want it to reach zero... then you have no protection from acids.

I would also take a look at viscosity and particulates.

Oil Analysis is predictive maintenance tool. Some use the information to extend drain intervals. If, your mileage is mostly highway miles you could consider increasing to 10K, if mostly city stop and go- I wouldn't. What are you really gaining by extending the drain interval. Our goal is to extend the life of the engine before a major overhaul, right?

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