What exactly is wrong with mixing brands?

[AP9]

I've read in various places that mixing different brands of oil should be avoided whenever possible, sometimes even recommendations of choosing one brand and sticking to it.

But why exactly is this?

Is it the difference in additive packages? If anything I'd think that could be beneficial, as one oil may have more of a certain additive and can thus make up for the lesser amount of that additive in another brand.

 

[actionstan]

I have been wondering this too.. I've read that when switching oils your car may burn more oil.. And that different additives can clash. I have no idea if there's any honest truth to those things.. I just traded in a 2003 buick century with 189k miles on it and the engine was plenty strong. I had it since 70k miles and most of its life it lived on whatever oil walmart put in it, Orange Cans of Death(fram) and I always topped off with super tech.. Until I started doing my own oil changes.

I'm pretty sure with my buick I commited all of the bitog sins. But engine wise it seemed pretty healthy and clean and I feel the car will probably fall apart around that engine if the next owner maintains the car


Edit: I should mention that typically I am a "purist" when I buy oil for my saturn that burns oil, I always buy a extra quart of the same brand and weight(typically maxlife) not based on scientific evidence but based on the warm fuzzy feeling to gives me lol

 

[901Memphis]

Nothing wrong with mixing if you are doing modest intervals, but Ashland products would dilute the wonderful sopus products calcium content since they use sodium.

Additive packages are balanced by each blender, so it's a good idea to mix within the same brand but it won't hurt anything except your TBN. This would only be apparent on extended drains.

Everything varies by application but all api sn oils are miscable.

 

[BlueOvalFitter]

I have been mixing oils for years. In fact, I will be mixing some in the near future.
I had a 97 F150 that had Chevron Supreme 10W30 mixed with ST 10W30 and 5W30 synthetic oiL its first 138K miles. After I sold it to my friend he would mix whatever he had, was on sale, or given to him to try. He even mixed Kendall Nitro 70 with ST 5W20 conventional in it once.
BTW, it has 228K miles on it and runs great!

Be careful, the anti-mix police here frown down on mixing oils.
Do you use an oil filter for multiple OCIs?

 

[Hyde244]

Nothing.

All proper oils are API certified, and can mix with any other certified oil - even older certifications like SM.

 

[Garak]

Originally Posted By: AP9
But why exactly is this?

Mixing oils bugs me, so that's the prime reason to avoid it.

Realistically, all API licensed oils are required to be miscible. Personally, I take that to mean that if I'm a quart low at the gas station, tossing in any licensed oil isn't going to cause any serious concerns; I don't take it as a license to mix just for the sake of mixing. Some have a pretty good idea what they're doing and what they're trying to accomplish when they blend, and are often trying to get a certain set of viscometrics.

That doesn't mean you can get the "perfect blend of oil" by mixing Mobil Super's sodium additive package along with PYB's high moly and calcium and a little race oil for ZDDP and a little HDEO for thickness and a little Motul for ester and finish it off with Amsoil SS for that long drain feel. There is no shortage of oil brands and types available on the shelf; I have no reason to mix.

 

[901Memphis]

I don't frown up mixing but i wouldn't set to mix unless i was going to try a caterham blend or something similar. Some people just mix for the fun of it with no research other than gut feeling.

If you are using stuff that you got on clearance/sale/FAR or something similar go for it, but don't set out to mix 5 different quarts of stuff to make something better than is already on the shelf like Garak mentioned.

Topping off is another story, i would top off with whatever was around, although i prefer high calcium products to replenish TBN, if i had some VWB around i would use it.

I was just discussing mixing for the sake of mixing. If your going out to 5 different stores to make a frankenbrew you might be doing something wrong.

 

[Kuato]

Unless you're a chemist* it likely makes absolutely no difference.












* I am NOT a chemist.

 

[dgsbikes]

The only things "wrong" with mixing oils:

* Oil A is ABC Certified and Oil B is not - mixing both gives you a non-compliant (or partially compliant depending on how one sees it) product. While this may not damage the engine immediately, extremely prolonged use may not be optimal for the engine. It definitely voids the warranty unless one is ready to unquestionably prove the mixed oil chemistry was not a factor into the cause that triggered the warranty claim.

* Trade-Offs - For ex. Mixing a non extended mileage with an extended mileage oil will shorten the mileage span of the mixed oil to somewhere between that of the non-em and em oils mixed. This may be moot if the OCI goal is to use the mixed oil only to the mileage extent equal to the lower of the oils mixed. But the mix may extend better viscosity and HTHS characteristics than individual oils alone. As long as the trade-offs in some areas to benefit in other areas are acceptable, the trade-offs are moot as well.

A special type of trade-off would be an additive potentially rendered suboptimal due to or lack of presence of another in non-synergistic quantities. Again, a trade-off that may be acceptable in most cases.

Mixing a less tangy lemonade with a more tangy one may result in a perfect blend for some tastes, while others may prefer the less or more tangier ones. Neither options are destructive but some options may not optimally satisfy one's taste buds! And then the options are exponentially numerous when one factors in the color, salt levels, sugar levels , etc. into the two original lemonade blends! Some may prefer the saltier standalone while others may prefer the sweeter standalone while yet others may prefer a mix somewhere in between! The result is still a drink that is within a broader lemonade spec!


Personally, I may be trying the Caterham mix or an adaptation there of in my Honda Ody EX-L the goal being to increase OCI with a higher HTHS oil with decent VI to boost mix over an otherwise acceptable baseline oil.

 

[fdcg27]

Most add packs are more alike than different.
We've all heard of non-metallic adds that aren't dectected in a VOA or UOA, but we also know that most blenders are buying their add packs off the rack, so to speak, from a limited number of suppliers. I can only think of three, although I'm sure there must be more.
Still, if I were intentionally mixing, I'd try to match add pack metallic elements. IOW, I'd avoid mixing an oil with a sodium based add pack with one using no sodium.

 

[BlueOvalFitter]

Originally Posted By: BlueOvalFitter
Be careful, the anti-mix police here frown down on mixing oils.

Break out the anti-riot gear.

 

[Eddie]

This is only a guess: Oil is supplied with a certain percentage of additive "A" to achieve a certain level of performance. If I dilute that level by adding another oil then the original oil can't achieve the intended performance. One doesn't need a chemist to figure that out. However; people mix different oil all the time and I can't remember reading about a problem. Gear oil manufactures do state NOT to mix gear oils. Just my take on the subject. Ed

 

[CarbonSteel]

Originally Posted By: Garak
Originally Posted By: AP9
But why exactly is this?

Mixing oils bugs me, so that's the prime reason to avoid it.

^^^^ This; but other than that, I daresay I have never read or heard of anyone mixing oils that had a catastrophic failure because of it.

 

[CharBaby]

I've been mixing oil for 40 years! Today, I just do it differently.

1st, I did it out of need, as I didn't have much money and I'd mix all oils together for an OCI often without changing the filter.

I have mixed 5 different brands all being a different weight.
I wasn't trying to out think the chemist who have designed the oils, just trying to keep my car running.

2nd...Fast forward to today, I mix differently:

I mix syn and dino at something like...2 qts syn/3 qts dino OR...I will ad an orphan qt or two, to the other oils in my stash to either balance out the stash, or finish up a particular oil/weight/brand, mostly dino oils.

3rd...other example is:

I'll mix 3 qts 5W20 with 2 qts 10W40, if this is what I have in my stash. Though, I always try to buy oils that meet all 4 of our vehicles recomendations. 5W30 covers 3 of 4 cars, temp dependant but, each OM mentions different grades(except one car).

4th...I often buy up a store shelf of discounted/discontinued oil(all held in high regard here at Bob's) or, use sales/rebates, you get the idea? Any oil from, 5W20, 5W30, 10W30 and sometimes 10W40/15W40 though not often. And I have no reason to buy 20W50. So, my stash can often rival the best

No, I don't want to see your pictures!

I have never had an oil related engine problem in all of those years. I have removed the valve covers and the oil pan(to eliminate leaks) as many of these vehicles(too many to list) have had several hundred thousand miles on'em. PERFECTLY CLEAN!

Mixing oil may not be optimum but, it certainly won't hurt anything IMHO! As long as the OCI's are reasonable and the oils are for motor vehicles. I have always used/mixed oils that are for my engines though, I have used many diesel motor oils in gasoline engines and, that's a good thing

And yes, I use one brand/grade/wgt often! Lately, I only mix orphans just to use'em up, again, mostly dino oils!

Would I buy a new BMW, Lexus or Mercedes' and just start mixing oils? NO, not really! If I do though, it'll be a couple different qts of synthetic oil that I'd have in my stash that meet their requirements.

 

[SLCraig]

Meh. I do frankenblends all the time. I've yet to see an issue.
I think at a chemist level there might be issues but for a guy like me who just changes the oil and drives, there hasn't been any apparent issues from mixing oils. Sometimes I just mix all of what I have left in jugs to make a fill for my car. At least it's all new oil and not ever "Bullseye" brand!

 

[AP9]

Interesting. I wonder if a mix something like either of these would go ok in an older vehicle? I'm giving serious thought to trying the latter.

1. 4 quarts synthetic 5W-30 SN : 1 quart conventional SH
2. 3 quarts Mobil 1 0W-40 : 2 quarts Quaker State Defy 5W-20

 

[Clevy]

Originally Posted By: BlueOvalFitter
Originally Posted By: BlueOvalFitter
Be careful, the anti-mix police here frown down on mixing oils.

Break out the anti-riot gear.

You quoted yourself then commented on it. Huh.

K. If mixing oils was an issue every engine on earth would be having problems. There is always some oil leftover in an engine after draining. So its truly a non issue.
Now mixing brands may not be ideal however it does no harm. Don't expect o do extended drains on a mix without data though.
I mixed various oils for years and its only been in the past couple years that I'm not trying to use up that leftover jug with this oil change and I've never had an oil related issue due to mixing.
I have lost an engine due to using the restore engine additive. I will admit using 2 cans and it completely plugged the oil filter.
Restore has no business in an engine you wanna keep

 

[zerosoma]

I try to mix within conglomerates. Such as SOPUS, Ashland, and Exxon-Mobil. If its Kendall I would mix Trop Artic too if I needed.

 

[Garak]

Originally Posted By: 2010_FX4
^^^^ This; but other than that, I daresay I have never read or heard of anyone mixing oils that had a catastrophic failure because of it.

For sure. It would take a lot of effort to produce a mix that could cause a catastrophic failure.

Imperial Oil road tar with M1 or something like that perhaps? Petro-Canada food grade lubricant with some Duron? Of course, those aren't mixes of API products with API products.

 

[TFB1]

Originally Posted By: SLCraig
At least it's all new oil and not ever "Bullseye" brand!


That Bullseye should have been named for what exits the other end of the bull...