# 5w-20 + 10w-40 = ?

#### asiancivicmaniac

Okay, I have 5 qts 5w-20 and 5 qts 10w-40 Proline dino. I originally was going to use the -20 in my mom's Camry and the -40 in my car for the Auto-Rx rinse phase but now I'm wondering if I will get close to a 30 weight if I mixed the two 1:1. Will there be any negatives?

#### Mr Nice

Mix it, there will be no negatives.

#### chevrofreak

It'll be a thick 5W-30, maybe close to a 10W-30.

#### Norm Olt

Well, it SURE ain't gonna' be a "15w-60" 5w +10w= 15w -20 -40= -60

#### StevieC

Originally Posted By: LT4 Vette
Mix it, there will be no negatives.
+1

#### glenncof

0.5x5 + 0.5x10 = 7.5 cold 0.5x20 + 0.5x40 = 30 hot if different than 50/50 just change ratio

#### asiancivicmaniac

Originally Posted By: StevieC
Originally Posted By: LT4 Vette
Mix it, there will be no negatives.
+1
great

#### ekpolk

Originally Posted By: Norm Olt
Well, it SURE ain't gonna' be a "15w-60" 5w +10w= 15w -20 -40= -60
NO!!! You can probably mix it without overt problems, but OTOH, remember that the calculation of the resulting net viscosity is not a linear calculation. There's a logarithmic formula for calculating the true net vis resulting after mixing oils of different viscosities. It's here on BITOG somewhere - find the true formula, and make sure you're OK with the outcome before actually mixing oils.

#### asiancivicmaniac

is there a name for that formula?

Originally Posted By: glenncof
0.5x5 + 0.5x10 = 7.5 cold 0.5x20 + 0.5x40 = 30 hot if different than 50/50 just change ratio
That would be the cold viscosity? I thought calculating it was a bit more involved? AD

#### Norm Olt

Originally Posted By: ekpolk
Originally Posted By: Norm Olt
Well, it SURE ain't gonna' be a "15w-60" 5w +10w= 15w -20 -40= -60
NO!!! You can probably mix it without overt problems, but OTOH, remember that the calculation of the resulting net viscosity is not a linear calculation. There's a logarithmic formula for calculating the true net vis resulting after mixing oils of different viscosities. It's here on BITOG somewhere - find the true formula, and make sure you're OK with the outcome before actually mixing oils.
Uh, my comment was 100% sarcastic, BTW...

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