Mixing oil

[Chadwilliam1]

I read the Oil University but I didnt get the answer directly. I searched but couldnt find exactly but I can imagine it has been asked before.

If you mix oil, say Mobil1 full synthetic.

If I mix 5w 30 and 10w 30 does it make 7.5w 30
or
0w 30 and 10w 30 does it make 5w 30? Assuming there are equal amounts.

Chad

 

[tinmanSC]

Originally Posted By: Chadwilliam1
I read the Oil University but I didnt get the answer directly. I searched but couldnt find exactly but I can imagine it has been asked before.

If you mix oil, say Mobil1 full synthetic.

If I mix 5w 30 and 10w 30 does it make 7.5w 30
or
0w 30 and 10w 30 does it make 5w 30? Assuming there are equal amounts.

Chad

Yes, you've got it. If you were to mix a 5w30 and a 10w30 you would get a thick 5w or a thin 10w (there is no 7.5w).

Same with a 0w-x and a 10w-x, you would end up with something in between.

 

[chubbs1]

If all things were equal yes but things like VI can change that and make perfect blending a little harder. I am sure smarter people than me can chime in but there are variables. Generally though, If you mix say M1 5w20 and 5w30 you will have a thicker 5w20 (or thinner 5w30). 1 more thing, oil will usually shear fairly quickly in many engines.

 

[CATERHAM]

First there is no such grade as a 7.5w30.
You'll either end up with a heavier 5w30 or lighter 10w30.
The 0w30 and 10w30 mix might produce a 5w30 but you may not really know.

But you're asking the wrong question since SAE grades are a range of viscosities and you're mixing two ranges with an indeterminate outcome.
In mixing oils it's best to know the KV40, KV100 and HTHSV of each oil and then you've got a pretty good idea what you'll end up with using a viscosity mixing calculator as follows:

http://www.widman.biz/English/Calculators/Mixtures.html

 

[GROUCHO MARX]

Around these parts we call it blending, pardner.

 

[mongo161]

Mixing and/or Blending.....it's all good.

 

[Chadwilliam1]

I see, I knew there was not a 7.5w 30 but for the sake of argument.

I realize I was just looking for a simplified answer of a complicated question but you guys helped me out.

Thanks

Chad

 

[Trex101]

Just read that mixing different oil will contributed to the deterioration of pumpability performance. Mixing might not be a good idea anymore.

Check out this thread: https://bobistheoilguy.com/forums/posts/2374150/

 

[bepperb]

That deterioration wasn't from mixing oils per say. The takeaway from that would be that mixing a good cold pumpability and some leftover poor cold pumpability resulted (unexpectedly) in oil with poor cold pumpability. Not that mixing two oils with good cold pumpability could result in bad cold performance.

Sure, mixing some 0w30 and some 10w30 will certainly give you a 30 weight oil at the end of the day. It would probably have a low temp performance in the 5-30 range. Mobil is the only oil company I know of that gives and OK to mix grades in their FAQ's, which I've always thought was odd.

 

[CATERHAM]

Originally Posted By: bepperb
Mobil is the only oil company I know of that gives and OK to mix grades in their FAQ's, which I've always thought was odd.

RL also actually encourages the mixing of all their oils to fine tune the viscosity to your own particular application and that includes their street oils with their race oils.

Joe Gibbs does for their race oils as well.

 

[Garak]

Originally Posted By: CATERHAM
RL also actually encourages the mixing of all their oils to fine tune the viscosity to your own particular application and that includes their street oils with their race oils.

Joe Gibbs does for their race oils as well.


I suspect RL is quite careful with their chemistry to make sure there isn't any additive clash. As for Joe Gibbs do they mention anything about mixing four parts water to one part oil to make their atrocious pricing a little more palatable?

 

[CATERHAM]

Originally Posted By: Garak
Originally Posted By: CATERHAM


I suspect RL is quite careful with their chemistry to make sure there isn't any additive clash.

Don't think they're careful at all, it's simply is a non-issue.
All street motor oils today must be compatible with each other so additive clash is not a possibility.

The only remaining area of possible incompatability in blending different brands remains with some race oils and the makers of these oils will tell you.
For example Joe Gibbs race oils are not to be mixed with anything else including there own street oils.

 

[A_Harman]

Originally Posted By: Trex101
Just read that mixing different oil will contributed to the deterioration of pumpability performance. Mixing might not be a good idea anymore.

Check out this thread: https://bobistheoilguy.com/forums/posts/2374150/


This was an interesting thread, and the main point I took away from it is to be careful mixing oils to effect the W-rating, not that all mixing of oils is bad. It is best to mix oils that are from the same manufacturer and have similar formulation. Mixing to achieve a targeted high-temperature viscosity is safe and predictable when using a calculator such as Widman's. But if you want to mix a 0w30 and 20w50 to get a 10w40, you might get something that behaves unpredictably when it comes to cold start pumpability at -30C (-22F). If you expect to be doing cold starts at those temperatures, it would be safer to just buy a 10w40 and use that. Save the mixing for when you get out of winter.

 

[Garak]

Originally Posted By: CATERHAM
Originally Posted By: Garak
Originally Posted By: CATERHAM


I suspect RL is quite careful with their chemistry to make sure there isn't any additive clash.

Don't think they're careful at all, it's simply is a non-issue.


I think I overstated my case. I wasn't speaking so much about the additives actually "clashing" as if mixing race/street oils as you point out. I meant more that the additives are still fully optimal (i.e. avoiding dilution of intended ZDDP or moly content), and nothing beyond that.