M1 0W-40 Stash - Some SM/CF and SN

[e40]

I have a 24 qt stash, 4 of those are older, probably about 2 years old. 24 quarts is 4 oil changes for my Audi 2.7T, I'm wondering if I can mix the old stock and not throw off UOA results too far. (I just got the car, so no UOA yet) As the title says, the old ones are API SM/CF and the new bottles are SN.

I'm wondering if I should just put all 4 in at the next change and sample the next run. Or, perhaps use 1 quart old to 5 quarts new for each change?

 

[dparm]

I wouldn't really mix the SM and SN. Won't hurt, but why not just use it as it was originally intended?

 

[CATERHAM]

If you're concerned about determining the amount of viscosity loss from the virgin oil in a subsiquent UOA you can still calculate the KV100 from whatever mix proportion of the SM/SN oil that you ultimately use.
From memory the SM oil had a KV100 of 14.2cSt and the SN KV100 is 13.5cSt. And yes the SN oil is heavier than the SM oil due to it's higher HTHSV of 3.8cP.

 

[e40]

Thanks for the info.

A little background on the situation, I had a '99 A4 with the 1.8T, 4 quart sump. I sold that car about a year ago and kept those extra 4 quarts of M1/SM thinking I'd get another euro car eventually. A year passes, and here I am with the 2.7T, a 6 quart sump. So, I took advantage of a local sale acquiring the additional 20 quarts of M1.

It's been running Castrol Syntec 5w40 on 5K OCI's for the last 3 years, 48k miles.