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5w20 + 5w40 = 10w30? #5125914 06/05/19 11:45 AM
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PandaBear Offline OP
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Reason for asking: Scored some $10.97 Valvoline MST 5w40 recently, had a bunch of 5w20 Valvoline Synthetic from last year's discount. Based on data sheet it seems like they are 66cst/13cst and 44cst/8cst. So if I mix them 1:1, am I correct that it should come out to around 50cst/10cst? In that case it should be a Xw30 oil for cheap.

Would that make sense? Anything I'm missing? It would be for a warm climate car (90F in the summer high and 45F in the winter low).


"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah
Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125917 06/05/19 11:50 AM
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Actually, that would be 5w30, however the add pack between the two blends will be different. I would recommend running the 40 in the warmer months and the 20 during the cooler months and not mix them. Just my .02


2018 F150 5.0
2016 Ford Fusion 2.5
Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125923 06/05/19 11:58 AM
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Yes, it will probably be a 5W but there is no guarantee, just as there is no guarantee it will meet any of the approvals or certifications listed on either container. It will be a safe mixture however since ASTM D6922 provides for miscibility.


1994 BMW 530i, 251K
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Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125927 06/05/19 12:06 PM
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I've been wondering about that question.. how to figure out a frankenmix. That said, I don't see how adding a 5w to a 5w gets you a 10wX???

Re: 5w20 + 5w40 = 10w30? [Re: Mad_Hatter] #5125929 06/05/19 12:08 PM
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Originally Posted by Mad_Hatter
I've been wondering about that question.. how to figure out a frankenmix. That said, I don't see how adding a 5w to a 5w gets you a 10wX???


PPD's and base oil blends. What base in oil 1 might require x amount of PPD's may not remain the same for oil 2, so you end up with insufficient PPD for the end blend to meet the W rating that either of the independent constituents held.


2019 RAM 1500 Sport - Mobil 1 EP 0w-20, FRAM Ultra
2020 Grand Cherokee SRT - Ravenol SSL 0w-40, FRAM Ultra
Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125941 06/05/19 12:16 PM
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How different are the additives between 5w40 MST vs 5w20 "Advanced Full Synthetic"?


"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah
Re: 5w20 + 5w40 = 10w30? [Re: OVERKILL] #5125943 06/05/19 12:17 PM
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Originally Posted by OVERKILL
Originally Posted by Mad_Hatter
I've been wondering about that question.. how to figure out a frankenmix. That said, I don't see how adding a 5w to a 5w gets you a 10wX???


PPD's and base oil blends. What base in oil 1 might require x amount of PPD's may not remain the same for oil 2, so you end up with insufficient PPD for the end blend to meet the W rating that either of the independent constituents held.


Got it... So if I understand that right, in practice there's no real way to know what the end result is without testing it but as a rule of thumb it's going to be lower than each constituent or as low as the lowest constituent oil???

Does it have that same effect on the upper viscosity rating also? (for both the low and the high of a multi vis?)

Last edited by Mad_Hatter; 06/05/19 12:26 PM.
Re: 5w20 + 5w40 = 10w30? [Re: Mad_Hatter] #5125951 06/05/19 12:26 PM
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Originally Posted by Mad_Hatter
Originally Posted by OVERKILL
Originally Posted by Mad_Hatter
I've been wondering about that question.. how to figure out a frankenmix. That said, I don't see how adding a 5w to a 5w gets you a 10wX???


PPD's and base oil blends. What base in oil 1 might require x amount of PPD's may not remain the same for oil 2, so you end up with insufficient PPD for the end blend to meet the W rating that either of the independent constituents held.


Got it... So if I understand that right, in practice there's no real way to know what the end result is without testing it but as a rule of thumb it's going to be lower than each constituent???

Does it have that same effect on the upper viscosity rating also? (for both the low and the high of a multi vis?)


Correct.

The impact on the hot side of things is much more predictable, as you are primarily just dealing with VII's. It's the cold side of things where you dealing with trying to mitigate wax crystal formation that things get more difficult, as different bases can have wildly different cold temperature behaviours.


2019 RAM 1500 Sport - Mobil 1 EP 0w-20, FRAM Ultra
2020 Grand Cherokee SRT - Ravenol SSL 0w-40, FRAM Ultra
Re: 5w20 + 5w40 = 10w30? [Re: OVERKILL] #5125958 06/05/19 12:30 PM
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Originally Posted by OVERKILL
Originally Posted by Mad_Hatter
Originally Posted by OVERKILL
Originally Posted by Mad_Hatter
I've been wondering about that question.. how to figure out a frankenmix. That said, I don't see how adding a 5w to a 5w gets you a 10wX???


PPD's and base oil blends. What base in oil 1 might require x amount of PPD's may not remain the same for oil 2, so you end up with insufficient PPD for the end blend to meet the W rating that either of the independent constituents held.


Got it... So if I understand that right, in practice there's no real way to know what the end result is without testing it but as a rule of thumb it's going to be lower than each constituent???

Does it have that same effect on the upper viscosity rating also? (for both the low and the high of a multi vis?)


Correct.

The impact on the hot side of things is much more predictable, as you are primarily just dealing with VII's. It's the cold side of things where you dealing with trying to mitigate wax crystal formation that things get more difficult, as different bases can have wildly different cold temperature behaviours.


Makes sense...tx👍

Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125962 06/05/19 12:31 PM
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You are quite welcome.


2019 RAM 1500 Sport - Mobil 1 EP 0w-20, FRAM Ultra
2020 Grand Cherokee SRT - Ravenol SSL 0w-40, FRAM Ultra
Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5125968 06/05/19 12:33 PM
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What vehicle is it going in?

Re: 5w20 + 5w40 = 10w30? [Re: ad244] #5125972 06/05/19 12:34 PM
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Originally Posted by ad244
What vehicle is it going in?


Haven't decided yet, either 08 IS250 or 97 Integra.


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Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5126033 06/05/19 01:34 PM
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It is NOT linearly additive. So it is not as straight forward by simply averaging the values.
It is probably closer to the 5w-30, though.

IIRC, there is a calculator here somewhere at BITOG.


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Re: 5w20 + 5w40 = 10w30? [Re: JMJNet] #5126036 06/05/19 01:35 PM
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Originally Posted by JMJNet
It is NOT linearly additive. So it is not as straight forward by simply averaging the values.
It is probably closer to the 5w-30, though.

IIRC, there is a calculator here somewhere at BITOG.


Now that would be neat/useful...👍

Re: 5w20 + 5w40 = 10w30? [Re: PandaBear] #5126045 06/05/19 01:39 PM
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I certainly wouldn't worry about this mixture of two known good oils.
I've run Mobil 0W40 mixed with MileSyn 0W20 in my Caddy V6 (specc'd for 5W30) and it hasn't blown up yet.

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