Originally Posted by Talent_Keyhole
Originally Posted by OVERKILL
Originally Posted by Triple_Se7en
But Yes..... you can even blend 20w50 with 0W20.
It's all compatible..... 15w40, 5w40, 10w50.....etc.... blend away. Even allowances with diesel/gas passenger oils/vehicles.
Any approvals that the former individual constituents held are now wholly invalid, as it was only the fully formulated product, as blended by the manufacturer, that passed the requirements for those approvals.
Every time a standard drain and refill occurs, 10-20% of the previous oil remains in the engine, especially newer engine designs with overhead cams, turbos, oil coolers, and VVT. If what OVERKILL says is true, then all of these approvals are made wholly invalid each and every time the oil is changed. I have documented that residual oil will reduce your viscosity, lower your TBN, increase oxidation levels, and retain upwards of 20% of wear metals, contaminents, fuel dilution, etc. The only way to prevent this is to perform a full volume oil change, thereby ensuring a 99% fluid exchange.
I'd say that particular issue is soundly mitigated (the mixing part torpedoing the integrity of the certifications/approvals) by using the same product on each drain and fill which should ensure that a fresh fill on a post-OCI event is simply dealing with left over contaminants. This is also why when doing UOA's one wants to trend multiple OCI's to allow the oil to "settle" as different oils plate-out differently and can use vastly different ad packs, the components of which may compete on wear surfaces. So it takes time to determine what "normal" is for a given oil.
Now, oil manufacturers do of course change formulas, but I'd expect the additive side of things will remain mostly the same with some of the primary differences occurring in base oil selection, which should essentially be a non-issue. This somewhat ties back to the OP's situation where the 5w-20 and 0w-20 are probably identical save the base oil and VII treat rate.
I'd expect the risk of anything happening switching brands at an OCI as approaching zero due to the low volume of the oil being mixed at that period. This, and having to add a top-up oil of a different brand during an OCI is what the miscibility standard is really designed to deal with, ensuring that when somebody does have to mix, they don't risk catastrophic failure by the two oils adversely interacting. This is quite contrary to the narrative spun by the pro-mixing crowd who believe that at minimum there will be absolutely no negative interactions and that they are potentially somehow producing a superior product.
