Mixing oils - what viscosity do you get?

[Kuato]

So it's been asked numerous times here, what viscosity do you end up with when you mix oils of different viscosities?

Well to help answer this question, a 50/50 sample was sent to Blackstone.

Here's the report:

I think Blackstone is in error, the resulting viscosity of 11.74 doesn't read as a 40 (min 12.5 CST required) but rather a thick 30 (9.3 - 12.5 CST). I've got an email in to them to clarify this point and hopefully will have an answer soon.


It'll be interesting to see what brands and viscosities people think went into the sample. I'll post up the answer tomorrow afternoon.

 

[JimPghPA]

One thing to keep in mind when you mix oils, is that when it gets cold enough the winter performance is not anywhere near an average of the first numbers. This is because if a molecule changes from a liquid to a wax at a certain temperature it will still change at that same temperature regardless of the other molecules around it. If for example you mix a 5 W- XX with a 20W-XX then the molecules from the 20W that change to a wax at a certain temperature will still change to that wax at that same temperature but now those wax molecules will be sounded by more molecules that do not change to a wax ( from the 5W ) so you end up with a sludge, that may still be pumpable or may not pump well depending on the concentration. It is a strange concoction of wax and oil and can best be called a sludge or similar to a Slurpee drink if you have a lot of the molecules that change to a wax. But also it is not a solid wax until it gets cold enough for the 5W molecules to also change into a wax.

 

[Kuato]

Absolutely correct. So no one who mixes should rely on any cold weather performance better than the highest xxW rating used.

What's your guess Jim?

 

[RamFan]

Blackstone doesn’t utilize API viscosity ranges to establish the “should be” viscosity numbers. That’s likely why they’re saying it’s a w40 and not a w30.

I don’t agree with the practice, but it’s how they do it.

 

[MParr]

Looks like a good oil for small engines.

 

[m37charlie]

Look up Mr Widman’s site. He is a quality oil distributor in the lovely city of Sta. Cruz de la Sierra on the eastern side of the Bolivia Altiplano; in the tropical lowlands. He has an algorithm that I have saved for mixing miscible lubricants based on viscosity at: -5C, 40C, and 100C. I have found it extremely useful over the years and would like to visit him eventually.

 

[MParr]

@m37charlie
I’ve looked at his oil mix calculator. Some people may be interested. I’m not all that concerned about mixing new oil that I have leftover from oil changes. I have a 5 quart jug and dump in my excess new oil. I will be using it in my mower. I have 5w30 blend, 5w30 synthetic, 10w40 4T, 10w30 VR1, 20w50 VR1 and SAE 30 HD in there. My mower won’t know the difference.

 

[Kuato]

No guesses? Ah well, not as much fun as anticipated.

Oils mixed were 5w-20 and 20w-50.

I know BS doesn't test the low end but the high end matches the average of a 20 and a 50.

Widman's calculator is pretty close to the actual results.

 

[bbhero]

Maybe Amsoil SS 5w20 and Redline 20w50..

 

[Kuato]

Maybe Amsoil SS 5w20 and Redline 20w50..

Ah, you see me as a boutique guy

Both are Schaeffer. The 20w-50 is labelled as a racing oil, the 5w-20 is their 9000 synthetic.

After seeing these results I won't have any issue using these two combined.

Above 20F / -7C, that is.

 

[ripcord]

You might find this to be interesting:

Mixing viscosities | Widman International SRL

www.widman.biz

 

[Kuato]

You might find this to be interesting:

Mixing viscosities | Widman International SRL

www.widman.biz

Referenced above twice but thanks-

 

[CleverUserName]

I did this once with 10w30 and 15w40. Also sent the 50/50 blended sample to OAI for testing and paid extra for the 40c viscosity lab work so I could see the whole picture.

The results were within 2% of the Widman calculator so yes it’s accurate. The unknown is the actual winter rating, which I assume is still a 15w.

Edited to add: these were both the same brand and formula used for my mixing experiment. The results may still be searchable on the new site.

 

[Shel_B]

What happens when you mix two viscosities with the same W rating and different high ends, such as 0W-20 and 0W-30 or 0W-40?

 

[CleverUserName]

What happens when you mix two viscosities with the same W rating and different high ends, such as 0W-20 and 0W-30 or 0W-40?

I would think they would keep the 0w rating. I forgot to mention that I mixed oils of the same brand and formula so there would be no antagonistic effects. I still use this blend in my vehicles and it has always given me excellent results.

 

[kschachn]

I would think they would keep the 0w rating. I forgot to mention that I mixed oils of the same brand and formula so there would be no antagonistic effects. I still use this blend in my vehicles and it has always given me excellent results.

No not necessarily. They may, or they may not. It’s not predictable.

Another thing that is not guaranteed is that the resulting mixture will carry any of the same licenses, approvals or specifications that the original oils may have held. Even if you mix two oils with the same specifications or approval there is no guarantee that the mixture will meet the requirements for that approval.

 

[widman]

Look up Mr Widman’s site. He is a quality oil distributor in the lovely city of Sta. Cruz de la Sierra on the eastern side of the Bolivia Altiplano; in the tropical lowlands. He has an algorithm that I have saved for mixing miscible lubricants based on viscosity at: -5C, 40C, and 100C. I have found it extremely useful over the years and would like to visit him eventually.

Alaska is a pretty state. Enjoyed our travel around it in 85. I escaped the virus in Bolivia in August last year after 5 months of lockdown, and am waiting it out in Florida at the moment. Eventually I'll get back to arrange things and retire to Fl.

 

[Kuato]

No not necessarily. They may, or they may not. It’s not predictable.

Another thing that is not guaranteed is that the resulting mixture will carry any of the same licenses, approvals or specifications that the original oils may have held. Even if you mix two oils with the same specifications or approval there is no guarantee that the mixture will meet the requirements for that approval.

True that it's not guaranteed, but you have to agree it's not certain that the resultant oil would not meet those standards. As stated earlier, mixing a 20w and 5w it would be wise to plan cold temperature use around the 20w specifications. However in mixing a 0w with another 0w I'd be confident of -35F starts.


If you look at it from an anal and regulatory perspective, then no, a mix doesn't have the licenses and approvals due to the fact that the company making the product simply hasn't submitted that blend for testing and approval.

However if you take a common sense approach and are using oils from the same manufacturer it's safe to say that the blend is extremely likely to meet or exceed the required standard. You would think that mixing Mobil1 5w-20 and Mobil1 5w-30 for example would be safe. In fact don't you think that Exxon/Mobil would have issued some kind of warning by this day and age if there were any problems involved with mixing viscosities?

Add to that the number of "frankenbrew" oil reports and threads on here - with no deleterious effects - and that answers that.

 

[kschachn]

True that it's not guaranteed, but you have to agree it's not certain that the resultant oil would not meet those standards. As stated earlier, mixing a 20w and 5w it would be wise to plan cold temperature use around the 20w specifications. However in mixing a 0w with another 0w I'd be confident of -35F starts.


If you look at it from an anal and regulatory perspective, then no, a mix doesn't have the licenses and approvals due to the fact that the company making the product simply hasn't submitted that blend for testing and approval.

However if you take a common sense approach and are using oils from the same manufacturer it's safe to say that the blend is extremely likely to meet or exceed the required standard. You would think that mixing Mobil1 5w-20 and Mobil1 5w-30 for example would be safe. In fact don't you think that Exxon/Mobil would have issued some kind of warning by this day and age if there were any problems involved with mixing viscosities?

Add to that the number of "frankenbrew" oil reports and threads on here - with no deleterious effects - and that answers that.

Being safe is separate and different than meeting a performance standard, specification or approval. Safe is dictated by passing ASTM D6922 which is part of the SAE J300 requirements.

 

[Kuato]

Being safe is separate and different than meeting a performance standard, specification or approval. Safe is dictated by passing ASTM D6922 which is part of the SAE J300 requirements.

Sorry but by that logic, Amsoil and numerous other oils are "unsafe", which we know is not necessarily the case - I'm pretty sure you're not saying that Amsoil is unsafe to use, or are you? Not trying to start a fight, but insistence on a test being passed to be safe, well, passing a test isn't possible when an oil isn't submitted or put through that test.

In any case, let's fall back to the M1 discussion and my question, which you didn't answer: if, in fact, it was unsafe to mix viscosities, then wouldn't ExxonMobil, one of the largest producers of petroleum products in the world, have put out some sort of warning by now?