5w20 + 5w40 = 10w30?

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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).
 
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
 
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.
 
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???
 
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.
 
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?)
 
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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.
 
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...txðŸ‘
 
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.
 
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...ðŸ‘
 
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.
 
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.


The calculator won't give him the W rating though.

I believe the one you are thinking of is Widman's:
https://www.widman.biz/English/Calculators/Mixtures.html

Which gives us 10.19cSt @ 100C, 57.62cSt @ 40C, making it an xW-30.

Using the below values:
[Linked Image]

[Linked Image]
 
"it hasn't blown up [yet]".....‚...‚...‚


Full disclosure: guilty of that at times!...‚
 
There is no need to get a precise viscosity number calculated. Leave it to the junior chemists here to play with it. The final viscosity will surely land somewhere between the two oils. A 97 or even an 08 model vehicle will easily, and I mean EASILY be fine with this mix.
 
Originally Posted by userfriendly
"It hasn't blown up yet". The BITOG standard and what I base all of my experimenting on.



It's the BITOG standard for about half of us.

The other half lie awake at night worrying about particle counts on their oil analysis.
wink.gif


In 50+ yrs I've only had 2 motors really fail, one was a 327 Chevy where casting porosity caused an internal leak at one of the oil passages resulting in spinning a rod bearing and the other was a Chinese gen set that broke the exhaust valve head off.
 
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