Mixing Oil to top off?

[TorchMini]

I know it's been discussed before, but I can't find my specific issue here, so...
Is there anything profoundly wrong with adding a touch of, say Royal Purple 5W-30 to an engine that's on a load of 0W-20 from a different brand?
i.e. Do different oils interfere with each other or perhaps compliment each other?

 

[buster]

Not a problem.

 

[kschachn]

If the oil is API licensed or has independently passed ASTM D6922 then miscibility is guaranteed. Nothing else is guaranteed however, including carrying any of the approvals, licenses or certifications any of the individual oils may meet. Miscibility only means that they will not separate upon mixing and cause harm. The winter rating of the mixture is also not guaranteed nor is it predictable.

And no it is not complementary unless you are able to run the suite of tests in SAE J300 or in an approval sequence to determine that. Additive formulators do not operate by guessing and chance.

 

[jstert]

as long as your oil mixing doesn’t cross-stream you should be ok...


seriously speaking, if you are topping off, what is the alternative, driving around with a partially empty oil sump? i will take readonably close-spec’d mixed oil over insufficient oil any day.

 

[ATex7239]

No issue. I used to mix different brands and viscosities cause I was broke and didn’t know any better.... That was 20yrs and over 100K miles ago. The car I am referencing is still running with the factory engine today. Sold it to a family member who still has it.

 

[GON]

I often wonder this myself, and never had a clear understanding. Here is a cut and paste answer from a basic search:

Since motor oils are generally made from the same ingredients (base oil and additives), they are typically compatible when mixed. (The American Petroleum Industry actually requires that all motor oil made in the U.S. be compatible with one another.) The differences mostly come down to the oil refining process.

 

[Astro14]

Miscibility is one thing (you can mix them and they won’t separate out).

But weird, unpredictable things can happen when different additive chemistries are mixed. Changes in cold performance. Foaming. Lowered resistance to oxidation. So, sure, they mix okay, but they may not work well together.

I know, you’re always mixing a tiny bit when you change oil, but the leftover bit is a lot smaller than a whole quart of top off oil.

Personally, I prefer to top off with the identical brand and spec. E.G. Using Castrol 0W40 in the Volvo? It gets topped off with the same jug. And the next oil change will be the same Castrol 0W40.

Mixed is probably better than a quart low, and certainly better than very low.

But mixed is not as good as unmixed.

 

[wpod]

I don't know where people get the idea about the SAE / ACEA type quality oils not mixing with each other, but then I don't know why people that worry about that do not buy extra oil of choice they know they might need. Remember other than a fluke type of scenario there are only a handful of additive companies and base oil refining companies on the Earth . Mixability is required in the meeting the specification process.

 

[ATex7239]

Miscibility is one thing (you can mix them and they won’t separate out).

But weird, unpredictable things can happen when different additive chemistries are mixed. Changes in cold performance. Foaming. Lowered resistance to oxidation. So, sure, they mix okay, but they may not work well together.

I know, you’re always mixing a tiny bit when you change oil, but the leftover bit is a lot smaller than a whole quart of top off oil.

Personally, I prefer to top off with the identical brand and spec. E.G. Using Castrol 0W40 in the Volvo? It gets topped off with the same jug. And the next oil change will be the same Castrol 0W40.

Mixed is probably better than a quart low, and certainly better than very low.

But mixed is not as good as unmixed.

Subjectively, people don’t like it or recommend it. Objectively, it doesn’t alter anything in a way one could even accurately measure or analyze. Except maybe in high performance or exotic engines.

 

[nomas]

This is BITOG . There is always going to be the naysayers on anything less than total obsession . I can only guess at how many people have mixed oils with zero problems . Myself included .

 

[kschachn]

This is BITOG . There is always going to be the naysayers on anything less than total obsession . I can only guess at how many people have mixed oils with zero problems . Myself included .

Where are the obsessed naysayers you refer to in this thread?

What I've noticed when this oft-asked question comes up is that there are lots of responders that accuse others in the threads of saying things that they did not say.

 

[JMJNet]

The engine will NOT know the difference. LOL!!!

 

[Bottom_Feeder]

It's totaled.

 

[Astro14]

Subjectively, people don’t like it or recommend it. Objectively, it doesn’t alter anything in a way one could even accurately measure or analyze. Except maybe in high performance or exotic engines.

That's just not true. This isn't subjective at all. Actual results from actual testing say otherwise.

Even in low performance engines, chemical interaction of the additives may result in degraded performance. Not always, but may.

And you have no way of knowing that is happening in your low performance daily driver.

You really need to talk to some folks who formulate oil for a living. Different companies use different chemistries. Changing the mix of those additives can result in negative interactions.

There is a tendency on this, and other, forums to reduce chemistry to "calcium" or "phosphorus" or 'Moly" when chemistry is far more complex. The elemental (looking at elements only) analysis of a UOA, or a VOA, is like reducing computer code to letters of the alphabet.

Saying, well they're both calcium so they will work OK together is like saying, sure, that bit of code will work with this other bit code because they both have "D" in the language.

It's a ridiculous over-simplification of a complex set of interactions.

Without rigorous, complete, testing, you simply have no way of knowing if your mix will have negative interactions. It may work fine.

It may not.

But you cannot know without the testing, and wishful thinking and internet opinions won't change that.

 

[930.engineering]

I know, you’re always mixing a tiny bit when you change oil, but the leftover bit is a lot smaller than a whole quart of top off oil.

On my GTI's EA888 3G it's exactly one quart leftover (~0.9 l). Total fill is 6.6 l
while I change 5.7 l. Granted, our Mini's 'French' PSA engine is 4.2 and 3.7 l,
so just 0.5 l, but between 10 and 15 percent leftover seems quite common,
and that's not far away if not rather similar to a top-off.
While topping-off with different brand (and likely different add pack) oil isn't
ideal your engine very most probably won't notice any difference. Why waste
oil you have sitting in your garage provided it's appropriate for your engine?
Topping-off commonly happens near the end of the interval, rarely right after
the beginning. If it does you likely have other issues.
Virtually nobody uses to flush his engine when swapping to a different brand
during/before an oil change.
.

 

[PF52]

I once cleaned the garage and found enough leftover full quarts (and several half quarts) from four or five different brands that I had enough to do a complete oil change on my old S-10 pickup. I even found an old still-in-the-box Fram orange can filter there on the shelf. So I threw it all in the truck and it didn't seem to mind one bit.

 

[JeffKeryk]

Frankenbrews are made everyday. Every stinkin' day. Personally I have never heard of engine damage stemming from a mix of oil brands or viscosities.

 

[ATex7239]

That's just not true. This isn't subjective at all. Actual results from actual testing say otherwise.

Even in low performance engines, chemical interaction of the additives may result in degraded performance. Not always, but may.

And you have no way of knowing that is happening in your low performance daily driver.

You really need to talk to some folks who formulate oil for a living. Different companies use different chemistries. Changing the mix of those additives can result in negative interactions.

There is a tendency on this, and other, forums to reduce chemistry to "calcium" or "phosphorus" or 'Moly" when chemistry is far more complex. The elemental (looking at elements only) analysis of a UOA, or a VOA, is like reducing computer code to letters of the alphabet.

Saying, well they're both calcium so they will work OK together is like saying, sure, that bit of code will work with this other bit code because they both have "D" in the language.

It's a ridiculous over-simplification of a complex set of interactions.

Without rigorous, complete, testing, you simply have no way of knowing if your mix will have negative interactions. It may work fine.

It may not.

But you cannot know without the testing, and wishful thinking and internet opinions won't change that.

Sure, something could happen or performance could be degraded.. or absolutely nothing could happen

There is a point of diminishing returns with analysis where it’s practicality and application to the real world become nonexistent. Lot of coulds and maybes, but to what end are we talking here.

 

[PimTac]

Why not just keep it simple? When you buy the Acme oil for your change pick up a quart of the same thing for top off. Then there are no doubts.

 

[buster]

I only advise mixing for temporary reasons otherwise I prefer keeping the chemistry the same.