Additive Clash

The term "additive clash" is quite a broad description that could encompass myriad possible outcomes. It might be an unwanted interaction between detergent types (for example salicylates and sulfonates together can cause issues if not done well), it might be the combination of large numbers of surface-active ingredients (like antiwear, FMs, detergents, metal passivators etc) that get in each others way and prevent good performance, it might be the combination of different polymers (VM, PPD etc) that cause unwanted cold temperature effects, or it might be any other unwanted interaction between active ingredients.

There's no way of knowing what is in any specific oil and what it might or might not do when mixed with another, especially in the real world. By this I mean that it is possible to run compatibility tests between oils (although nobody has run every combination of every oil in every ratio at every temperature), but this would be in a clean lab, in clean glassware, at prescribed ratios and temperatures. Throw in real world conditions - moisture, fuel, engine parts, wear metals, combustion products, heat cycles etc and there's no way to predict what will happen.

Luckily most oils use additives of similar chemistries - the industry has sort of ended up in the same pool of resources and so major 'clashes' between oils is rare (the early days of synthetic oil pioneering did cause some issues and led to the enduring myth that synthetics and minerals shouldn't be mixed). As has been stated upthread, the likely outcome is not disastrous but maybe just sub-optimal, but in a way you may never notice.
 
Yup, that's my position on the matter as well. You are far more likely to produce a product that performs worse than the individual products that you are mixing than one that performs better.


Yeah....

We ain't exactly mixing up a dry rub for cooking beef ribs or pork ribs here.

No sense in jacking up a perfectly balanced great oil with a different oil and adding Lucas oil stabilizer...

That'd be like adding lots of alum, ginger and a lot of vanilla to a pre made great beef rib or pork ribs rub.

Equals.... Horrible results.
 
ASTM D6922 involves mixing a test oil with six reference oils and subjecting the mixtures to a specific cycle of low and high temperatures over time. The mixtures are then evaluated for changes in appearance such as color, phase separation, and precipitation. Assuming the six reference oils are representative of varying oil formulations in the marketplace, passing results do not indicate or imply anything about changes in the performance of such mixtures in an engine other than failure due to substantial additive interactions is unlikely. Various aspects of engine performance may be impacted negatively or positively by such mixtures in the field, but given the lack of known major problems, probably not to a great degree.

Oil formulations are balanced, and as every experienced formulator knows even small changes can produce surprises. Positive surprises are the basis of patents, and there are a lot of oil patents. The D6922 test does not eliminate all risk from mixing oils, but does help reduce risk to an acceptable level, i.e. no catastrophic failure.
 
ASTM D6922 involves mixing a test oil with six reference oils and subjecting the mixtures to a specific cycle of low and high temperatures over time. The mixtures are then evaluated for changes in appearance such as color, phase separation, and precipitation. Assuming the six reference oils are representative of varying oil formulations in the marketplace, passing results do not indicate or imply anything about changes in the performance of such mixtures in an engine other than failure due to substantial additive interactions is unlikely. Various aspects of engine performance may be impacted negatively or positively by such mixtures in the field, but given the lack of known major problems, probably not to a great degree.

Oil formulations are balanced, and as every experienced formulator knows even small changes can produce surprises. Positive surprises are the basis of patents, and there are a lot of oil patents. The D6922 test does not eliminate all risk from mixing oils, but does help reduce risk to an acceptable level, i.e. no catastrophic failure.
I thought it was quite shocking to read in the SAE paper referenced by AEHaas that in the non-critical tests for there to be a concern, the manufacturer had to have a >95% confidence that failure would occur. That seems like an awfully low bar to pass, especially when it’s essentially self-policed. Personally I would think the concern should become priority if the possibility of failure exceeded 50% (essentially doubling the risk of failure, right?) but then again I’m not an oil engineer, either.
 
I spoke to both Red Line and Motul reps about five years ago. No, I'm not going down the boutique hole, I use Pennzoil Pearl River blend (a fine aromatic coff...oh, wait...). Both told me, notice the hear-say, that cleaning agents in the add pack can strip off other additives from previous fills lamination on parts. Those cleaning agents *wear out* (are used quickly) and deposition of the new add pack begins. I have no idea the truth of that but it sounded semi-reasonable at the time. It made more sense for esters in my opinion but, again, I can not vouch for any of it.
 
I spoke to both Red Line and Motul reps about five years ago. No, I'm not going down the boutique hole, I use Pennzoil Pearl River blend (a fine aromatic coff...oh, wait...). Both told me, notice the hear-say, that cleaning agents in the add pack can strip off other additives from previous fills lamination on parts. Those cleaning agents *wear out* (are used quickly) and deposition of the new add pack begins. I have no idea the truth of that but it sounded semi-reasonable at the time. It made more sense for esters in my opinion but, again, I can not vouch for any of it.
An older XOM engineer from years ago posted on here that this effect can also be attributed to short run oil consumption spikes when moving from one brand to the next. I believe he called it "seating".
 
You think this a problem just wait until you're nearly 80 and someone mixes your brands of bottled water. Holy bank is going to break loose!
 
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Because it increases the risk of additive clash.

The great the degree of mixing, the greater the risk of additive performance degradation through negative interaction. So, the higher the percentage of adulteration, the greater the degradation.

Multiple additive packages in one mix increases the chances of negative interaction.

So, the frankenbrew, a mix of several oils, has the highest risk of all, through multiple additive packages, with increased opportunity for negative interaction, and a higher degree of adulteration on each oil type.
Is this really a concern when mixing API oils of the same spec?
 
When you change your oil there is a significant amount that never is able to be fully drained. I've been changing my own oil and buying whatever 0W20 is on sale. I've never had an issue with mixing different brands of oils that are of the same weight and spec or with backward compatible specs - i.e. GF-5 or GF-6.
 
When you change your oil there is a significant amount that never is able to be fully drained. I've been changing my own oil and buying whatever 0W20 is on sale. I've never had an issue with mixing different brands of oils that are of the same weight and spec or with backward compatible specs - i.e. GF-5 or GF-6.
Yes that's what passing ASTM D6922 gets you.
 
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