Mixed Oil Debate

[kschachn]

API rated oils are tested to make sure the additives play nicely together. Mix away if you want.

API licensed oils are, or others that have an approval or license that mandates passing ASTM D6922. Otherwise bets are off without proof.

And it only means they are miscible and will not cause harm, it does not mean anything else after that. No guarantees of meeting any license, approval or specification the individual oils meet nor does it mean the mixture will have any particular winter rating.

That answer should be enough for any serious question but we all know how serious this OP is.

 

[Blinker]

API licensed oils are, or others that have an approval or license that mandates passing ASTM D6922. Otherwise bets are off without proof.

And it only means they are miscible and will not cause harm, it does not mean anything else after that. No guarantees of meeting any license, approval or specification the individual oils meet nor does it mean the mixture will have any particular winter rating.

That answer should be enough for any serious question but we all know how serious this OP is.

Yeah if the your engine needs a certain engine builder specification then mixing oils is probably it a good idea, I would agree.

 

[rob1715]

Mix away and you get 2.7W34.2569875

 

[kschachn]

Post a thread like this and you usually get a bunch of nonsense.

 

[OVERKILL]

API rated oils are tested to make sure the additives play nicely together. Mix away if you want.

They are mixed with a group of reference oils to ensure they don't split or do anything unexpected. They are in no way tested to confirm they retain all of the same performance characteristics they had when initially tested.

The biggest risk from mixing is a potential significant impact on the Winter rating. That's the most likely characteristic to be affected.

In the past, some oils have used significantly different additive package chemistries, for example, Valvoline used sodium, while nobody else did. Currently, Ravenol uses Tungsten while other manufacturers use moly. I'm sure you can recall Castrol and Kendall using Titanium. Some will use tri-nuclear moly (Mobil/Shell) while others may use more traditional forms of moly that require a higher treatment rate to achieve the same effect. They may also use different types of VII polymers.

While the potential for significantly negative synergies is quite low, upsetting the carefully selected balance of additives, particularly when mixing oils from different vendors that use different chemistries is not going to result in an improvement in performance, you are essentially guaranteed to have made something worse but it's unlikely that you'd ever notice it or that it would be significant.

Edit: I see @kschachn beat me to this bit, so I'm essentially reiterating, lol.

 

[jqgz]

If you mix oils you get the highest of the winter ratings and an unpredictable resultant hot viscosity somewhere between the two. 5w-20 and 10w-30 turn to 10w-20 at the thick end of the 20 spectrum. Mixing 5w-20 and 0w-40 would not be good in my opinion. It's not going to balance at a 5w-30. If you mix rocks and sand you don't get gravel.

 

[Shel_B]

API rated oils are tested to make sure the additives play nicely together. Mix away if you want.

Are you able to support that statement? I know that the oils are supposed to be miscible, but nowhere have I read that the additive packages will "play nicely together." What do you mean by that?

 

[Blinker]

The API ensures that oils of the same API spec are compatible with each. If mid-way through your OCI you’re down a quart of oil and you don’t know what brand of oil the shop used, do you really think you’re causing harm by pouring a quart of oil that’s a different brand? I mean come on now. I’ve never heard of any motor oil company say you can’t mix with other brands. The only thing I’ve read from motor oil companies remotely regarding this is if you are using an extended mileage formula. Extended mileage formulations such as, Mobil 1 extended performance, Castrol Edge extended performance, and Amsoil Signature Series, cannot guarantee the long drain interval if topping off with a different motor oil.

Which brings me to another point. Pennzoil has a new oil called Pennzoil Top Off Oil. It was mentioned here once and I saw it on the Shell product guide about a week ago. Do you think Pennzoil is going to market something that is going to cause some sort of chemical imbalance?

 

[CharBaby]

Jesus Christ what did you raid the oil drain bin at the local Autozone to come up with all those different grades?

YES!
Ever since I discovered BITOG's "product, rebate, sales" section.

Years ago(I mean like 40 & 50 yrs ago), when I had no money, I would use any oil in my cars just to have clean oil.

*This last mix that your referring to was from a friend who was cleaning out his garage and had a bunch of unopened oils leftover. Some from his motorcycles & tractor and such, so he gave'em to me and I was happy to take them. I mean, if you're going to throw'em away/recycle them, I'll use'em in something.

 

[demarpaint]

Can you mix 50/50 the leftovers for another fill, like Pennzoil 0w20 and Castrol Edge 5w40? Both exceed the service grade for the vehicle.
What exactly do you get with this mix, a 2.5w30 ?

It's funny how often these threads come up. You can mix the two, however the math doesn't work like that since there is no such grade as 2.5w30. If I had to venture a guess you'd probably end up with a 5w30. A VOA would tell you for sure.

 

[FordMan59]

Speaking of beaten to death oil subjects, I think we need a good ole fashioned 5W20 VS 5W30 Thread!
Opinions?

Neither one, 10w40 conventional in any flavor. Though it's not done often if I get down to 1 or 2 qts of the brand I've been using in a specific car I don't waste it, I mix it on the first oil change with whatever new brand I'm going to start using in that particular car. It's all going to be 10w40 though.

 

[kschachn]

It's funny how often these threads come up. You can mix the two, however the math doesn't work like that since there is no such grade as 2.5w30. If I had to venture a guess you'd probably end up with a 5w30. A VOA would tell you for sure.

It won't show that.

 

[ka9mnx]

If you have left over oil after an OCI, you bought too much. If you have left over oil, put it in you lawn mower.

 

[demarpaint]

It won't show that.

TIA- It wouldn't give a viscosity for the mix? In otherwords EG: 10.6@100C, then you look at a chart and know the grade of the oil? I realize there's a range for a 20 grade, 30 grade, etc. and not "in between grades" like an imaginary 2.5w30 people think they created. Which was the point I was making.

 

[wemay]

The API ensures that oils of the same API spec are compatible with each. If mid-way through your OCI you’re down a quart of oil and you don’t know what brand of oil the shop used, do you really think you’re causing harm by pouring a quart of oil that’s a different brand? I mean come on now. I’ve never heard of any motor oil company say you can’t mix with other brands. The only thing I’ve read from motor oil companies remotely regarding this is if you are using an extended mileage formula. Extended mileage formulations such as, Mobil 1 extended performance, Castrol Edge extended performance, and Amsoil Signature Series, cannot guarantee the long drain interval if topping off with a different motor...

So you're saying it only matters with extended drain oils? What if someone mixes Valvoline syn (no mileage claim) with regular Mobil1 (guarantees 10k mi)? Or, a syn with a conventional? Where is the line drawn and why?

 

[4WD]

Are you able to support that statement? I know that the oils are supposed to be miscible, but nowhere have I read that the additive packages will "play nicely together." What do you mean by that?

IMO the best chance for that is to 1.) use a small amount like a leftover quart in 8 an quart change 2.) same brand.
For example I have tossed in some M1 EP with M1 AFE in same viscosity … not exceeding recommended OCI of the AFE.

 

[Hogwash]

I know some might say there's a big difference between a small engine and a vehicle engine. But I've been mixing for years. All of my scraps go into my "mower jug". Doesn't matter the type or weight....it all goes in there. It's got everything from 0/20 synthetic to 10/40 conventional and everything in between in there.

I haven't bought oil for my mower or pressure washer in a very long time. And neither engine seems to care one bit. In fact, I add less makeup oil to the mower engine these days than when I did abiding strictly to the recommended 5/30 synthetic.

 

[Blinker]

So you're saying it only matters with extended drain oils? What if someone mixes Valvoline syn (no mileage claim) with regular Mobil1 (guarantees 10k mi)? Or, a syn with a conventional? Where is the line drawn and why?

Ignoring.

 

[kschachn]

TIA- It wouldn't give a viscosity for the mix? In otherwords EG: 10.6@100C, then you look at a chart and know the grade of the oil? I realize there's a range for a 20 grade, 30 grade, etc. and not "in between grades" like an imaginary 2.5w30 people think they created. Which was the point I was making.

Not for the winter rating which is what you were highlighting.

 

[demarpaint]

Not for the winter rating which is what you were highlighting.

My bad, I should have made it 2.5w35 to be safe from our resident experts like yourself. Again my bad, I should have proof read it better!! Thanks for bringing it to my attention.