What viscosity do you end up with when you mix?

Joined
Jun 3, 2021
Messages
1,238
Let's say you were to mix one quart of 5W-30 with one quart of 20W-50.

Do both quarts effectively flow like a 20W-50 now because that half of the mix is slower to flow and basically "blocks" the flow of the 5W-30, or do you essentially create a 10W-40 with the two different viscosities averaging out?
 
Let's say you were to mix one quart of 5W-30 with one quart of 20W-50.

Do both quarts effectively flow like a 20W-50 now because that half of the mix is slower to flow and basically "blocks" the flow of the 5W-30, or do you essentially create a 10W-40 with the two different viscosities averaging out?
What two quarts of oil are you desiring to blend? Be brand and viscosity specific for each. Reason-being are the wide variations with 5w30 oils.
 
What two quarts of oil are you desiring to blend? Be brand and viscosity specific for each. Reason-being are the wide variations with 5w30 oils.
I'm not asking for centistokes, I mean in general what does the outcome look like. Has nothing to do with brand.
 
Let's say you were to mix one quart of 5W-30 with one quart of 20W-50.

Do both quarts effectively flow like a 20W-50 now because that half of the mix is slower to flow and basically "blocks" the flow of the 5W-30, or do you essentially create a 10W-40 with the two different viscosities averaging out?
The base oils blend as do the VII's and the PPD's so you end up with an overall heavier base oil blend than the 5W-30 and a lighter one than the 20W-50. The resultant KV100 is easily calculated, but the Winter grade is more difficult because of how bases behave below 0C as wax crystal formation starts. While there was sufficient PPD content to make a light (probably 4cSt) base oil pump low enough and stay light enough to pass CCS at -25C, the 20W-50 likely had a much heavier base which, even with the PPD's, will still skew the overall blend heavier and thus carries a potentially heavy (no pun intended) penalty on the Winter grade performance testing.

So, you could end up with a 15W-40 for example.
 
Brand of 5w30 tells me a name to look up. Can't hash any numbers until you get more specific X 2.
OVERKILL is right. It's likely too thick to be 10w40 and likely falls under 15w40.
 
The base oils blend as do the VII's and the PPD's so you end up with an overall heavier base oil blend than the 5W-30 and a lighter one than the 20W-50. The resultant KV100 is easily calculated, but the Winter grade is more difficult because of how bases behave below 0C as wax crystal formation starts. While there was sufficient PPD content to make a light (probably 4cSt) base oil pump low enough and stay light enough to pass CCS at -25C, the 20W-50 likely had a much heavier base which, even with the PPD's, will still skew the overall blend heavier and thus carries a potentially heavy (no pun intended) penalty on the Winter grade performance testing.

So, you could end up with a 15W-40 for example.
Thank you, this is exactly the type of answer I was looking for.
 
Let's say you were to mix one quart of 5W-30 with one quart of 20W-50.

Do both quarts effectively flow like a 20W-50 now because that half of the mix is slower to flow and basically "blocks" the flow of the 5W-30, or do you essentially create a 10W-40 with the two different viscosities averaging out?
No exact science here but my math for simple sake says you end up with 12.5w40.

Simply stating
5 + 20 = 25 / 2 = 12.5
30 + 50 = 80 / 2 = 40
So 12.5w40

Of course this is not taking into account actual data just math.

Just my $0.02
 
No exact science here but my math for simple sake says you end up with 12.5w40.

Simply stating
5 + 20 = 25 / 2 = 12.5
30 + 50 = 80 / 2 = 40
So 12.5w40

Of course this is not taking into account actual data just math.

Just my $0.02
Except the 12.5 Winter grade doesn't exist. The Winter grades aren't specific viscosities, they are ranges defined by CCS and MRV, you cannot just perform that simple math on them and arrive at anything coherent.
 
12.5 wt. does not technically exist but thats not the point. TNT is providing a "seat of the pants" number that people can understand. I get it. He even said its "just math" and "not exact science". Its not meant to be technical.
This example is like measuring battery capacity in "miles" instead of kWh, it might seem "easier" but it's ultimately nonsense because it's trying to apply a static measure to a variable or range. You think you are helping by making it "simple" but ultimately, by avoiding the proper units, you are just furthering ignorance because the person doesn't leave the conversation with any greater understanding of the material than when they arrived.

There is no "seat of the pants number" because grades are clearly defined ranges in SAE J300, which has been posted countless times on this forum and should be the basic starting point for anybody interested in this subject.

Clearly, the OP appreciated a more detailed and accurate answer, given his response to my reply.
 
Last edited:
This example is like measuring battery capacity in "miles" instead of kWh, it might seem "easier" but it's ultimately nonsense because it's trying to apply a static measure to a variable or range. You think you are helping by making it "simple" but ultimately, by avoiding the proper units, you are just furthering ignorance because the person doesn't leave the conversation with any greater understanding of the material than when they arrived.

There is no "seat of the pants number" because grades are clearly defined ranges in SAE J300, which has been posted countless times on this forum and should be the basic starting point for anybody interested in this subject.

Clearly, the OP appreciated a more detailed and accurate answer, given his response to my reply.

And if you mix Castrol Syntec 5W-20 SM (9.1 CSt) with the 5W-30 (9.4 cSt)... Of course at that point does it really matter.
 
Let's say you were to mix one quart of 5W-30 with one quart of 20W-50.

Do both quarts effectively flow like a 20W-50 now because that half of the mix is slower to flow and basically "blocks" the flow of the 5W-30, or do you essentially create a 10W-40 with the two different viscosities averaging out?
No idea.
 
Back
Top