Yeah, that was the plan but my inner cheapness took over!

 

As a chemist who has spent 23 years formulating products including oils, I'll say additives from two different products don't always kick each other out but they definitely can and do. Years and six figures worth of money are spent making sure each oil formula is just right. Probably be okay just this once but taking a chance on a two year old 6.7 over a few quarts of oil?

 

I'm curious just what you believe will be "kicked out"??? I'm not a chemist, but I've been avidly involved in tribology related topics for more than a decade now. What you are proposing happens is something I've never heard of and I feel compelled to challenge the statement. Either you're going to teach me something new, or you're full of BS.

Generally, API licensed lubes have a very robust additive package; most all of which can be seen in VOAs. It is true that not all additives will show up in a VOA, but most will. You can see a wide variety of lubes here:
http://www.pqiamerica.com/
Here's the link to the HDEOs:
https://pqia.org/heavy-duty-diesel-engine-oil/
As you can see, there are a slew of lubes that all use essentially the same additives, but to varying degrees of concentration. Depending upon base-stock, there's only so much room for additives to stay in suspension. The products we buy today are blends of many things; there's no "pure" oil in the mass market from a consumer's standpoint. All lubes are blends. Typically, most all lubes have things like Ca, Mg, and many other elements; most of which are multi-purpose for things like anti-wear and detergency, etc. It's very typical to see one product brand have more Ca and less Mg, more boron but less Ti, etc. Each manufacturer takes a unique approach, but there's nothing in one brand that is going to kick out something from another brand. Some brands favor Ca over Mg; others vice-versa. Some favor Ti, boron or moly. These are all means to an end. There's phos, zinc, and a lot of other elements added to oil in varying amounts all to reach a goal. Some manufacturers choose to use moderate amounts of many additives; some choose to use a more heavy concentration of fewer elements.

My point is that there's not anything I'm aware of that's going to "kick out" something from the lube; given that any host base-stock has a finite limit of suspension, as you add more volume, the ratios stay the same. Mixing Delo with Rotella or Delvac isn't likely to cause a major malfunction of the lubes. Further, the API specifically states that mixing their approved/licensed products in the correct application does not cause concern; it's safe to do. There's too much for me to cover here, but this is their direct link:
https://www.api.org/products-and-services/engine-oil

As long as the concentrations stay at/near the same, there's nothing that's going to happen in terms of stuff falling out of suspension. If you use 5 qrts of a lube that has more Ca and less MG, then mix it with 5 qrts of lube that has more Mg and less Ca, all you end up with is a lube that has a a similar effect as those lubes with more balanced add-packs. Adding volume actually drives down the overall concentration of any one element when two products have dissimilar add-packs, but it also increases the overall holding capacity. Some brands favor more balanced add-packs; others prefer more pin-point approaches. Neither is wrong. Just two roads to the same destination; that of wear control and cleaners/detergents/anti-agglomerates.
Looking at Ca, Mg, Phos, and Zn .... (rounding to the nearest 50ppm)
Ford Motorcraft: 1500, 800, 1200, 1250
John Deere: 1450, 900, 950, 1050
Delo: 1500, 700, 700, 800
Delvac: 1800, 550, 800, 900
Rotella T4: 2050, 0, 950, 1050
DuronHP: 1100, 1000, 1050, 1200
Kendall SD XA: 1850, 400, 1100, 1250
These are not the only additives, just a smattering of the more prominent ones. Like I said, moly, Ti and others are also used. The point to understand is that a host lube can hold a total of "XYZ" additives in suspension, and so when you heavily dose it with ____, you have to back down on ______. But, as you add volume by mixing two different brands, the concentration may go down in one element, but gain in another. And as you can see, some brands balance their approach; others dose heavy to one end and ignore the other. But all these brands are known to do very well. When you mix brands/packages, all you are doing is blending more of what's already being blended and unless you know the specific elemental concentrations at the start, you really don't know if you're increasing or decreasing the concentrations. But you'll never go "over" the amount that the lube can hold in suspension, because the math does not work that way.

I will note that there are some additives which do not show up in VOAs, and so not all additives are going to be known except to the constructor/blenders as proprietary.

Additives cost money. So the companies are always in a balancing act between desired performance and desire profitability.

Mixing oils of similar nature (for example CJ-4 Delo and CK-4 Rotella) isn't going to cause the additives to "kick out" each other. What it will do is make for a more difficult time to analyze the lube in terms of the unique brand effectiveness if you're trying to use UOAs. When you blend to brands of lubes (or even different API classifications), it just makes it nearly impossible to distinguish the effects of certain elements in terms of wear control, etc, relative to the specific package you're trying to track. But that's not at all detrimental to the engine; the lube will still protect and clean as designed.

So, using the VOA examples above, let's say you wanted to mix Rotella with Deere ... and you're going to mix it 50/50
The resulting average concentrations would be thus:
Ca=(2050+1450)/2 = 1750ppm
Mg=(0+800)/2= 400ppm
Phos=(950+950)/2= 950ppm
Zn=(1050+1050)/2= 1050ppm
The math precludes the concentrations ever going out of bounds from a standpoint of totality.
Ironically, the result of mixing the Rotella and Deere comes somewhat close to the OEM blend in the Delvac; not exact, but close. There are a huge slew of brands out there; some are unique, some are just copies of others. But they ALL do a great job of protecting the engine. If you were to only mix 2 qrts of Rotella with 8 of the Deere, the concentrations would be altered, but they would NEVER go above the values of either host lube, and therefore would never be in a concentration high enough to "kick out" another element.

Now, like I said, I'm not a chemist. But the API and other chemists I know, some of whom directly contract their services to the additive industry leaders like Lubrizol, etc, have told me that mixing lubes is not detrimental generally. It just muddies the waters if you're trying to get a delineation of performance in UOAs. If you can prove to me that there's specific evidence that shows blending common HDEOs will cause things to "kick out" others, then by all means, educate me please.