Bad Mixes and Boutiques

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Jan 29, 2006
I am new to BITOG and have learned a lot by reading old posts. However, I am still very confused about "standards" in additives. I read the April '76 Popular Mechanics article provided in another thread, and I was surprised to read repeatedly in the article that in the '70s certain additives were found to be incompatible with certain synthetic bases. Specifically, zinc dithiophosphate CAUSED severe cam/lifter wear when added to an undisclosed synthetic base. In similar threads here, I have seen Terry dismiss "bad mix" conclusions (granted, sample size of one) and follow up with the conclusion that "bad mixes" do exist (Redline and M1).
I assume that a "bad mix" could be either an imbalance that doesn't perform optimally, or an incompatibility in which an additive precipitates or reacts with another component. I am not concerned much about imbalances (I rarely utilize the full life span of oil anyway). However, I am concerned about incompatibilities.

1) Does anyone know what base oil was found to be incompatible with ZDP (CAS# 19210-06-1)?

2) Is "don't mix" addvice just be on the safe side or has anyone observed a repeatable, known incompatibility?

3) Could someone unintentionally create an incompatibility by making a "homebrew", combining additives, or mixing old and new oils?

4) Do standards exist that would prevent a boutique oil formulator or even a racing oil formulator from using an additive package that would be incompatible with other oils on the market? Can Mobil really know that their oil is compatible with Motul for example?
I have re-read the article mentioned above. It was in Popular Science, not Popular Mechanics. I have found part of the answer to my question number 1. The ZPD incompatibility was with diester base oils. (quote from Robert Reubusch, Emery Industries).

Am I the only one curious about whether additives from different companies might not be compatible and if so, how/why?
Well, I may be talking to myself, but I can add a little more to this story. According to Citgo's web site, they say: "Mixing brands is not the best practice because the additive systems in each may be different and when mixed may not function as efficiently as desired. However, no serious problems will occur if you must add a different brand of equivalent quality between oil changes."

At face value the answer from Citgo appears to be that oils of "same quality" can be mixed with no incompatibilities. I don't really know the definition of "same quality". So I don't know what this means.

My conclusion is that the detergents (metal salts) are somewhat taylored to the base oil based to a degree on solubility. So, I think that if an incombatibilty exists, it would be when a detergent was at the edge of solubility in one base oil and then was mixed with a different base resulting in precipitation of the detergent. Likewise, one may see a problem when a very polar ester and certain detergents are used together as aftermarket additives.

But then, what do I know?
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