Admittedly, I had never heard of this concept until a few years ago. And I can’t seem to find much on it except that it is a possibility. I thought part of the API standards was a requirement for compatibility with other oils of the same rating, as well as backwards compatibility? Both of my vehicles get a variety. The Ford is a lease that I use for work, so it gets whatever the quick lube I take it to uses. Which changes frequently. And the Toyota gets whatever oil is on sale at the time or if I’m too busy to do it myself whatever the quick lube or dealership uses. The Toyota 2.5L engine requires 4.8 quarts but I only fill it up to 4.5 quarts or so. The remains make it into a 5 qt leftovers jug and will eventually go into the engine. This brew is a variety of 3 or 4 brands of both SP and SN + ratings. So is additive clash a real thing I should take into consideration here or is it a theoretical idea? Are there any published test or papers showing this has happened, what the consequences are or what mixtures should be avoided?
Additive Clash
- Thread starter ATex7239
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You would have to define "additive clash". Any oil that has an API license and any other oil that has passed ASTM D6922 is guaranteed to be miscible with other oils that have passed the same test. However there is no guarantee that the resulting mixture will still meet any license, specification nor approval that the individual oils may meet. Neither does it have to meet the listed winter rating. It does mean that the mixture will not cause harm, separate or otherwise physically damage an engine.
It really has nothing to do with "backwards compatibility" or any listing of which mixtures should be avoided. It is only a last-ditch guarantee not to cause harm.
It really has nothing to do with "backwards compatibility" or any listing of which mixtures should be avoided. It is only a last-ditch guarantee not to cause harm.
Additive clash is certainly a real thing. It happens with industrial oils a lot. And can lead to large, expensive issues.
Additive clash for a PCEO product shouldn’t really happen. At most you’ll probably see some premature shearing - this comes from different VII’s. Which cause different shearing rates.
There is testing done. Most majors will just CYA and say mix with a max of 10-15% of old/other products. They won’t do testing of compatibility of say Mobil and Pennzoil. Afton might do basic compatibility testing with Lubrizol, on their PCEO line up. That sort of thing. But it’s going to be enough to just CYA and put a disclaimer up.
Here’s a paper on changing over of products, on a more large scale:
www.stle.org
Additive clash for a PCEO product shouldn’t really happen. At most you’ll probably see some premature shearing - this comes from different VII’s. Which cause different shearing rates.
There is testing done. Most majors will just CYA and say mix with a max of 10-15% of old/other products. They won’t do testing of compatibility of say Mobil and Pennzoil. Afton might do basic compatibility testing with Lubrizol, on their PCEO line up. That sort of thing. But it’s going to be enough to just CYA and put a disclaimer up.
Here’s a paper on changing over of products, on a more large scale:
Best Practices
www.stle.org
For PCMO it is not the same issue. But it also doesn't mean it is necessarily a good or beneficial idea for the reasons I listed above. Some people on here have the misguided illusion that they have the blind ability to "blend" oils to achieve some higher goal.Additive clash is certainly a real thing. It happens with industrial oils a lot. And can lead to large, expensive issues.
Additive clash for a PCEO product shouldn’t really happen. At most you’ll probably see some premature shearing - this comes from different VII’s. Which cause different shearing rates.
There is testing done. Most majors will just CYA and say mix with a max of 10-15% of old/other products. They won’t do testing of compatibility of say Mobil and Pennzoil. Afton might do basic compatibility testing with Lubrizol, on their PCEO line up. That sort of thing. But it’s going to be enough to just CYA and put a disclaimer up.
Here’s a paper on changing over of products, on a more large scale:
Best Practices
What is not the same issue?
Industrial oils are different, right? Same with turbine oils.
Yes. Additive packages can be very different from brand to brand. Gear oils are especially… difficult, too.
That’s why I said at the beginning of my post, it’s not a big deal for PCEO’s. You can see some premature shearing. But that’s about it. If you’re not pushing your engine oils limits and you’re not doing oil analysis, then not a big deal.
The majors will still cover their own butts and say don’t mix with more than 10-15% of another product. They released this memo at every major formulation / spec change. They did it with SP/GF6 and they did it with D1G3. Several also did it in the rapid formulation changes we saw late 2021/early 2022 with product shortages. This is a CYA thing is all.
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I happened to change out the factory rear diff oil in my '21 GMC when HPL was having the open house. I found a layer of gray sludge in the bottom of the housing and sent wwillson a photo of it and he showed one of the engineers there who said it was definitely an additive incompatibility straight from GM. HPL gear oil went in after cleaning the gunk out.
It’s real. It shows up in lab testing. It’s hard to predict.
It can degrade the performance of additives that, while miscible, conflict with each other’s chemistry.
When industry insiders have measured it, and PhD chemists talk about it, I wouldn’t be so quick to dismiss it.
Motor oils are "formulated" which is a fancy way to say that the engineers balance the ratios and types of additives added to base oils to get the effects they are trying to achieve. Mixing different "recipes" together can result in lower performing oils. An analogy would be mixing two different brands of yellow cake mix together to make a cake. It will come out of the oven looking like cake, but it may not be as good as either would baked separately.
That said, I have mixed brands of motor oil a bazillion times without noticeable ill effects to use up left over oil or to approximate the weight of oil I want if I don't have the right stuff on hand. My OBS Ford is running a mix of 0w-20 and 20w-50 as I was out of 5w-30 at the time. It won't notice the difference on the way to the lumber yard and back.
That said, I have mixed brands of motor oil a bazillion times without noticeable ill effects to use up left over oil or to approximate the weight of oil I want if I don't have the right stuff on hand. My OBS Ford is running a mix of 0w-20 and 20w-50 as I was out of 5w-30 at the time. It won't notice the difference on the way to the lumber yard and back.
Is that what miscible means? I wouldn't have assumed more than the oils staying mixed at any temperature and not forming layers or emulsions.
I'm pretty sure you know the defection of miscibility as do I, but the extension into not causing harm is part of the ASTM test objective:
I don't think most oils have special additives that can't be mixed with other oils.
Worst case scenario, the additives may not function optimally.
Worst case scenario, the additives may not function optimally.
Yes but that pretty much tells me it only has to stay homogenous. There doesn't seem to be any test to determine "it functions properly". And you can't, viscosity can be severely impacted and can have disastrous results.
But given similar viscosities, or reasonable mixes to achieve a certain viscosity range I don't expect any issues
But given similar viscosities, or reasonable mixes to achieve a certain viscosity range I don't expect any issues
Nothing is stopping to make a PAG based engine oil, well besides ASTM D6922 maybe. PAG may or may not be miscible with hydrocarbons
Yes but an additive package is only certified as-formulated, whether that be a license or approval.
And are we saying the same thing? I never claimed there was any functional test to any resulting oil mixture.
The only caveat to this is that motor oils are formulated to a performance and profit target.
So it is theoretically possible to have a better oil, and as such a market for boutique oils and additives exists.
I don't really see much of a point in mixing 2 fully formulated oils though. That to me would generally be counterproductive.
This. Very small changes can return measurable differences in results. It is always best to avoid mixing oils. It’s not likely you will blow anything up. It’s also likely that a mixture could provide a lower performing product than what each would do individually.
interesting for sure + i sometimes mix like others but usually same brands as my 2001 300 hp TT with a 4.25 qt sump gets redlines 15-50 + 15-40 at change time but as needed in the summer only 15-50 Red is added. rarely used in the winter its a garage queen but like my motorcycles an enjoyable fresh air drive in nicer weather
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