Originally Posted by gsxr

Soot level is not the only reason to change the oil. Everyone seems to forget about TBN, additive levels, viscosity breakdown, sump size, filter capacity, and all that other pesky stuff. 3-5kmi OCI's are fine with dino oil of the proper API rating, for normal service, no oil analysis required. It never hurts to change more often if you want. At the other extreme, changing the filter annually and topping off (never actually changing the oil) is ridiculous.

If you want to do extended OCI's, knock yourself out, but recommending that for basically everybody else on the forum is not smart. You don't know their car, what oil they are using, their driving habits, oil consumption rate, engine condition, etc.


As I've repeatedly stated, for the record, I personally do extended OCI's (10kmi) on my cars, with analysis every time including TBN and F-soot, and only with Group IV/V synthetics. Analysis indicates I could probably go longer but 10k happens to be a convenient interval for me. That's just my preference. Y'all can do whatever you want.