Originally Posted By: cheesepuffs
Originally Posted By: md6040vr6t
Originally Posted By: cheesepuffs
Originally Posted By: LotI
Don’t go out and buy 20’s or 30’s as the M1 is a thin 40 and will become a 30 in short order, as mentioned. If you already have it, then mix away.
I thought full syns didn’t really sheer and only need to be changed because the additives deplete?
They can and do. Note that there a few different “levels” or groups of synthetics. They may sheer slower than conventional oils, but you can find charts for how a lot of oils lose weight during average driving. Many variables such as the specific oil in use measured up against the driver’s driving habits, air quality, engine condition, etc. Some guys replace the filter and keep the oil going a while longer. Every car is kind of it’s own unique configuration and it’s cool that we have UOA to help us make informed decisions for the specific condition of our engine. I just usually do 7500 oil changes in Honda because I’m using better oil and filter than stock and the manual calls for 7500 mike changes with conventional. It could probably easily go 10,000, but I do a lot of city driving and cold starts.
Your previous post right before this one suggests that in actual practice synthetics really don’t shear during a remotely normal length OCI?
Not aimed at you now, but in general, I feel like this place has been full of a lot of contradictory information lately. I’ve literally read here before that synthetics don’t shear out of grade, they just need to be changed due to TAN and also detergents being used up. And then we get some people saying just use M1 40 weight because it shears down to a 30 weight like nothing anyway. And then we get an answer like it will shear but not for forever anyway. Where does the truth lie? Again, not picking on you but on the whole forum lately it’s been like this. PAO cleans, PAO doesn’t clean at all. Group designation matters, group designation doesn’t matter at all. NOACK is super important, no wait it’s actually not something we should judge an oil by now. This place seems to be trending away from facts and more into speculation and sometimes even wild opinion. Just my observation.
Quite simple:
Anything with VII's can and will experience some viscosity loss due to shear. Whether that's countered by viscosity gain due to oxidation or accompanied by viscosity loss due to fuel dilution is where things get changed up and vary significantly on engine, application and how it is operated.
An oil with no VII's cannot shear (there's nothing to shear). But it can still experience viscosity loss due to fuel dilution or gain due to oxidation.