Mixing Oils for Desired Viscosity Index

[buster]

Most people are aware that while oils are compatible, many use different detergent/additive systems and should not be mixed. It is best to stay within the same brand when possible.

It does not hurt if you switch brands often, or occasionally mix in different brands, but you're not getting an optimal oil and you are only getting an uknown.

The case for improving VI falls along the same line of thinking.

"When you mix golf balls and basketballs, you don't get softball sized spheres - you get a physical (not chemical), mixture of golf balls & basketballs. When you mix a low molecular weight oil with a high molecular weight oil you get a physical mixture with molecules of different sizes. The extreme temp properties of those mixtures can't be determined "a priori" (theoretically), only by experiment." - TS

 

[Swissdieselfan]

Very correct, if you mix oils the result is an unknown. Quite why anyone mixes oils in the first place is hard to comprehend. There are plenty of different oils available, so if you have a particular requirement there is no need to play at being an oil chemist.

 

[ARCOgraphite]

What if you want a mid-high saps 0w20?
Non Boutique brand.

 

[oilmaven]

I'm not aware of any damage resulting from mixing different brands of oil (there have been a few "Frankenbrew" UOA's on here where the user mixed whatever odds and ends were available and the results were fine...sorta like making soup when you clean out the refrigerator). I prefer to stick to one brand and viscosity appropriate for my vehicle.

 

[danthaman1980]

oh hooey. Motor oil isn't made up of softballs - nor is it made up from molecules of one single molecular size or molecular weight. Using your comparison, motor oil is already made up of 'golf balls and basketballs'. If I want a lighter oil I can simply add oil with a few more golf balls/fewer basketballs than the oil I'm using... for a heavier mix I can add oil with a few more basketballs/fewer golf balls than the base oil in question. How do you think the oil manufacturers achieve target viscosities in the first place?

True, for predictable results it is best to use oils of the same basestock and additive chemistry - and there is no way to tell EXACTLY what you end up with unless you test the blend... but (basestock and additive chemistry alike), if I mix a quart of 10cSt oil with a quart of 12cSt oil, guess what - I may not end up with exactly 11cSt oil, but it will for sure be somewhere between 10 and 12.

 

[ARCOgraphite]

I wanna know what the vis is at 15C. I wish API required data at "ST&P". And yes I can use the calculator but with the advanced polymerics there is NO substitute for test results.

 

[bama7x57]

I'm currently mixing Nexgen 5w20 with Nexgen 10w40. 3 qts of each in a 6qt sump. It's the weights I bought for dirt cheap.
I'm guessing it's about 7.5w30, but I really don't know. I'm not concerned either. I'm been mixing different brands and weights for years and never had any engine troubles on my vehicles listed in my sig as well as others.

 

[gfh77665]

Originally Posted By: Swissdieselfan
Very correct, if you mix oils the result is an unknown. Quite why anyone mixes oils in the first place is hard to comprehend. There are plenty of different oils available, so if you have a particular requirement there is no need to play at being an oil chemist.


I have no desire to mix oils, nor play Chemist. I do want to blend off some oils I got nearly free, but that are not of the optimum viscosity. I have two cases of 30wt. I am blending off 2 or 3 at a time with 5-30's, shooting for something in the 10-30 neighborhood.

The facts I live in a hot climate, and all of the oils are Pennzoil yellow bottles, are in my favor. Sometimes, its just necessary to mix is what I am saying.

 

[Donald]

Originally Posted By: Swissdieselfan
Very correct, if you mix oils the result is an unknown. Quite why anyone mixes oils in the first place is hard to comprehend. There are plenty of different oils available, so if you have a particular requirement there is no need to play at being an oil chemist.


+1 what he says. WHY??

 

[bama7x57]

Originally Posted By: Donald
Originally Posted By: Swissdieselfan
Very correct, if you mix oils the result is an unknown. Quite why anyone mixes oils in the first place is hard to comprehend. There are plenty of different oils available, so if you have a particular requirement there is no need to play at being an oil chemist.


+1 what he says. WHY??


In my case, I can change the oil in all my vehicles for about for about $7 each including filter and still get 300K+ miles without any oil related issues. WHY NOT??

 

[needsducktape]

Originally Posted By: bama7x57
I'm currently mixing Nexgen 5w20 with Nexgen 10w40. 3 qts of each in a 6qt sump. It's the weights I bought for dirt cheap.
I'm guessing it's about 7.5w30, but I really don't know. I'm not concerned either. I'm been mixing different brands and weights for years and never had any engine troubles on my vehicles listed in my sig as well as others.


Same here, found them on clearance at wal-mart for $2 a qt.
My Subaru calls for 5-30 but given its easy life as a commuter (10 highway miles each way)the blend should work for an oil change or two.

 

[CATERHAM]

Originally Posted By: danthaman1980
oh hooey. Motor oil isn't made up of softballs - nor is it made up from molecules of one single molecular size or molecular weight. Using your comparison, motor oil is already made up of 'golf balls and basketballs'. If I want a lighter oil I can simply add oil with a few more golf balls/fewer basketballs than the oil I'm using... for a heavier mix I can add oil with a few more basketballs/fewer golf balls than the base oil in question. How do you think the oil manufacturers achieve target viscosities in the first place?

True, for predictable results it is best to use oils of the same basestock and additive chemistry - and there is no way to tell EXACTLY what you end up with unless you test the blend... but (basestock and additive chemistry alike), if I mix a quart of 10cSt oil with a quart of 12cSt oil, guess what - I may not end up with exactly 11cSt oil, but it will for sure be somewhere between 10 and 12.

You're on the right track.
Formulators can and do use different molecular weight oils to formulate a finished oil. Some advanced formulations use very heavy high VI PAOs instead or in addition to polymer VMs to achieve the final VI of an oil.

As far as blending finished oils of different viscosities is concerned, viscosity calculators do a pretty good job in predicting the final outcome including the oil's final viscosity index. That said kinematic viscosity spec's don't correlate well with actual operational viscosity in an engine consequently predicting HTHSV (bearing viscosity) is the best approach since that measure does correlate well to oil pressure.
So to know where you at in real terms you need an oil pressure gauge as well as an oil temp' gauge.

 

[Swissdieselfan]

Funny part of last post:
but it is possible that if you mix Red Line 0w20 with Mobil 1 0w40 for example, the additives and base stocks could provide better protection for your given engine better than either Red Line or Mobil can provide on it's own at any of their offered viscosities .

UMM, I must send that to Mobil R&D as they have a comedy section for their company blog!

You're more likely to be stuck by lightning whilst mixing a Redmob 0/30 hybrid brew than produce a good new oil.

 

[Phishin]

Originally Posted By: Swissdieselfan

UMM, I must send that to Mobil R&D as they have a comedy section for their company blog!

You're more likely to be stuck by lightning whilst mixing a Redmob 0/30 hybrid brew than produce a good new oil.


Please, by all means, send it their way.

If you took a poll, and looked at the opinions of all the real scientists on here....people with actual master's degrees or PhD's in chemistry, physics, engineers, etc. vs. the non-scientific folk on here, you'd see that most people who have science degress don't see any harm in mixing most oils together. I bet you'd see that trend....based on what I've seen/heard from people on BITOG. Just sayin'.

And I never said it was likely that you could create a better oil, but you might. Why can't you see the possibilities of gaining the benefits of one oil (high anti-wear additives for example) and the benefits of another (super high VI's for example) WITHOUT having something catastrophic, or even slightly harmful take place?

 

[buster]

Quote:
see that most people who have science degress don't see any harm in mixing most oils together. I bet you'd see that trend....based on what I've seen/heard from people on BITOG. Just sayin'.

And I never said it was likely that you could create a better oil, but you might. Why can't you see the possibilities of gaining the benefits of one oil (high anti-wear additives for example) and the benefits of another (super high VI's for example) WITHOUT having something catastrophic, or even slightly harmful take place?


Disagree. The scientists I've spoken with said, yes they are compatible, but what you end up with is unknown.

 

[buster]

Quote:
but it is possible that if you mix Red Line 0w20 with Mobil 1 0w40 for example, the additives and base stocks could provide better protection for your given engine better than either Red Line or Mobil can provide on it's own at any of their offered viscosities .


Dude, you don't know what you're getting. You're just guessing at that point. Those two oils use additives/chemistries that are nothing alike!

 

[CATERHAM]

Phishin well said.

I'm not arrogant enough to think I can improve the chemistry overall of two premium oils like RL and M1 by mixing them.
I do know I can increase the AW level of M1 by itself and that may be beneficial if the application called for it.

I think the main concern some have is a perceived detrimental effect of mixing oil from different brands. First the base oils of all motor oils are totally miscible except for some race oils. So the only concern potentially is how the additives of the different formulations interact. Most motor oil DI packages are very similar and of those that are possibly a bit unique, a quick call or email to the formulator will usually dispel any concerns.
Most for political reason will never outright sanction blending with an unknown brand but they all will advise that you need not be concerned in any way in switching to their brand from something else and vise versa even if as much as 25% of the old oil remains in the engine.

In mixing oils, what can be determined with certainty is the final viscosity of the blend and that includes the viscosity index.
As for the oil's additive chemistry, I'm sure there can be positive or negative synergies but IMO at the very least the blend will be no "worse" than the least additized oil that's used which seems to be the concern of some.

 

[Phishin]

Originally Posted By: buster
Those two oils use additives/chemistries that are nothing alike!


Buster, just do you know, I'm not trying to be disrespectful or rude. Honestly.

And this above quoted statement is the premise that all anti-mixers stand on. But the reality is, who cares if they are different? Why would that matter? Because they "may not be" compatible? As the Phish lyric says...."Maybe so, Maybe Not"...but I've never heard of anyone mixing two oils together and mixture is not compatible.

Just because oils use different chemistries, does NOT mean there will be problems caused my mixing the two different chemistries together. Yeah, each chemistry will be "diluted" by a percentage based on the ratio of them being mixed....but that isn't necessarily a bad thing either.

Why do all oils use several different molecules and atoms to combat friction? Why don't oil companies only add moly, or only add zinc, or only add boron, or only add titanium, or just antimony, or what about organic forms, like those found in Fuchs Titan 0w20? THEY DON'T!! They usually use a mix of several. Using your argument, this would be a bad idea. But it must not be...because your oil gods (scientists are Mobil, Castrol, Shell) are doing it!! Instead, you have different anti-wear components that are "competing" against eachother....some outperform others at high pressures, others at tight tolerences, others at high temperatures, etc. etc. But none of them are #1 under all conditions...so they put a bit of everything in there to cover all the different physical conditions found inside an engine.

Just because "chemistries" are different, does NOT mean something bad is going to happen. This is actually how oil formulations are created. By mixing different chemistries.

There is "nothing" magical about Shell using 100ppm Moly here or 40ppm Boron there. It's just the least amount they can use but still achieve some acceptable amount of lubrication/protection under their tests. The tests used and what is acceptable determines how much and what additives are used.

 

[danthaman1980]

Originally Posted By: Phishin
If you took a poll, and looked at the opinions of all the real scientists on here....people with actual master's degrees or PhD's in chemistry, physics, engineers, etc. vs. the non-scientific folk on here, you'd see that most people who have science degress don't see any harm in mixing most oils together. I bet you'd see that trend....based on what I've seen/heard from people on BITOG. Just sayin'.


Agreed - most mechanics/auto techs (my own brother included) have never operated a viscometer, don't know the difference between dynamic and kinematic viscosity, and don't know what cSt stands for. Kinda wish I still worked in a lab so I could test blends myself, but no matter. I can speculate with the best of 'em ; )

There are a thousand factors that contribute to what oil might work 'the best' in any particular engine. Any recommendation an engine manufacturer makes - or any motor oil a lubricant company manufactures - is a carefully engineered compromise between performance, cost, complexity, and availability. Many of us are willing to put in the resources to improve that compromise in whatever direction we see fit - that's why we're here.

 

[Swissdieselfan]

I'm certain that any educated person will think it much more likely that you will create a worse oil rather than a better one!
I can't think of any OEM that recommends a mix your own approach to engine oils, they just point out it is no big deal if you use the wrong top up oil.