mixing viscosities, a more enlightened approach

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253
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Boston
OK, a little while back, I thought that mixing 0W-30 and 0W-40 in equal amounts would give you a 0W-35. Well, now I realize that the N and M in NW-M oil represents a range, not an actual viscosity. So, instead, let's look at the actual viscosity of, in this case, 0W-30 and 0W-40 Mobil 1. From their website tech data at 100 degrees Celsius 0W-40 viscosity = 14.3 cSt 0W-30 viscosity = 10.3 cSt now if you combine these in equal amount, assuming that the resultant viscosity can be interpolated based on the amounts of each component oil, you'd get in this case (14.3 + 10.3)/2 = 12.3 cSt. Now, looking at the handy-dandy viscosity/grade chart on the BITOG front page, an SAE 30 grade oil has a viscosity range of 9.3 to 12.49 cSt. So in this case, we'd have a mix that is still a 0W-30, albeit on the heavy side. Nice summer brew, perhaps? Especially since UOA's tend to show M1 viscosities dropping after a few miles (then thickening back up again, according to some). So, for a mix of 3 parts 0W-30 and 1 part 0W-40, we'd get (3*10.3 + 14.3)/4 = 11.3 cSt, just thicker than the middle of the 30 weight range. Good winter brew? A valid competitor for the much touted but oh-so hard to find German Castrol 0W-30? OK... is this a better way to look at mixing viscosities? Discuss!
 

GSV

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696
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Utah
Well GC has been measured at or around 12.2 cst and I don't think your mix would score an A3 rating. [Cheers!] [Patriot]
 

bigpaulo

Thread starter
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253
Location
Boston
GSV, OK, so instead of a 3:1 ratio, use the 1:1 ratio, giving a 12.3 cSt viscosity (on par with 12.2, no?) As for being A3 rated, true... but I live in the Greater Boston area, and I haven't been able to find GC, and I've been keeping my eye out for it. This M1 mix might be a good substitute, and perhaps a good alternative for those who have been using M1 and don't feel like switching horses in midstream. PS [Patriot] for German Castrol? What's up with that? [Wink] [ December 24, 2003, 11:23 AM: Message edited by: bigpaulo ]
 
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1,533
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Ephraim
quote:
Originally posted by bigpaulo: -*-* OK... is this a better way to look at mixing viscosities? Discuss!
Whay Visc are you looking for>??? What is the reason for the change? Can you either use a heavier oil or a splash of VII ???
 

Patman

Staff member
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21,989
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Oakville, Ontario
quote:
Originally posted by dustyjoe1: ..actually been thinking of doing the same. if weighted average doesn't work. what is the right way to calculate. Anybody know?
Honestly, the only true way to calculate it would be to mix it and then send a sample in for analysis. Two oils of differing viscosities will have different levels of viscosity index improvers, and could react differently with each other.
 
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555
Location
south texas border
true, but if you take for example a g4 synthetic like m1 ...if I understand correctly, should not be much vi improver in the mix. isn't that one of the advantages of a g4 or g5 syn? So it follows that the old weighted average approach might not be too far off. now mixing dinos that is a different animal IMO.
 
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13,132
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By Detroit
Someone posted (I think on this website) that when mixing two fluids of different viscosities, the resultant mixture would always have a viscosity somewhere below the arithmetic mean. I believe someone on the same thread posted that in mixing two oils, one with a 40 SUS viscosity and the other with an 80 SUS, the 50/50 mixture was tested and had a viscosity of 50 SUS, which suggests a mix is significantly lower than the arithmetic mean.
 
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555
Location
south texas border
maybe something like {(vi*v2)/(v1+v2)}* 1.875 = new vis do you have any more data points like your 40 and 80 makes 50 to plug into the above relation to see if it works. I back engineered the above from your numbers. Need more data to verify that it works though. If it does, then a 20 mixed with a 30 in equal parts would be 22.5 vis. Any thoughts? [I dont know]
 
Messages
13,132
Location
By Detroit
quote:
Originally posted by dustyjoe1: maybe something like {(vi*v2)/(v1+v2)}* 1.875 = new vis do you have any more data points like your 40 and 80 makes 50 to plug into the above relation to see if it works. I back engineered the above from your numbers. Need more data to verify that it works though. If it does, then a 20 mixed with a 30 in equal parts would be 22.5 vis. Any thoughts? [I dont know]
Pretty neat equation Dustyjoe1. Here is the original thread where I heard all this stuff, including a post about a book that has a table listing the resulting viscosity for various mixing combinations. http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=004626#000016 [ December 26, 2003, 01:36 AM: Message edited by: TallPaul ]
 
Messages
555
Location
south texas border
Thanks, just a first attempt at trying to connect the dots. Definitely need more dots. Also I'm assuming a 50/50 mix and that its a linear relation... It can always be massaged a bit...but the main thing is It NEEDS MORE DOTS. Let me go and check out your link. Happy holidays. [Cheers!]
 
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