Mixing viscosities? Castrol and Valvoline say NO!

[webfors]

I spoke with a rep at Castrol and Valvoline today and they both categorically stated the following:

1. They do not recommend mixing viscosities. Not even, for example, Valvoline 4T Motorcycle oil 10w40 and 20w50.
2. They stated mixing different brands and versions of oils is fine as long as they are the same viscosity.
3. The outcome of mixing viscosities is unknown and does not follow the expected logic (i.e a result 15w45 from the example in #1).

I was surprised to hear the exact same answer from two different oil company reps.

 

[demarpaint]

I've read that here many times before. While it's OK to mix, in the case of different grades the outcome is unknown. Still people think they're going to concoct some special viscosity. That's not the case though.

 

[OilUzer]

Originally Posted By: webfors
...does not follow the expected logic (i.e a result 15w45 from the example in #1).


Ohh no, another mathematician! lol
I recently learned not to do math on W!

 

[RooflessVW]

Why would you mix grades to begin with? Seems there is already a broad spectrum available where every want/need is covered.

A common concoction is 50-50 M1 0W-40 and 15W-50...

And I just don't understand why.

 

[gathermewool]

Sounds ridiculous, saying that mixing brands is ok, but not different viscosities of the same oil.

 

[KevinP]

Every time you change the oil you mix products.

 

[RooflessVW]

Originally Posted By: KevinP
Every time you change the oil you mix products.

You change viscosities every time?

 

[blupupher]

You can get a ballpark of the oil weight if you know the cSt of each oil, but the W rating will be unknown.

People mix for a variety of reasons.
Using an old stash of different weights, trying to get specific properties of different oils, or just wanting to play around.

I know that mixing a 0W-20 and a 15W-40 will get me somewhere in the 30 weight range, and as for the W rating, I don't care here in south Texas.

 

[Triple_Se7en]

Originally Posted By: webfors
I spoke with a rep at Castrol and Valvoline today and they both categorically stated the following:

1. They do not recommend mixing viscosities. Not even, for example, Valvoline 4T Motorcycle oil 10w40 and 20w50.
2. They stated mixing different brands and versions of oils is fine as long as they are the same viscosity.
3. The outcome of mixing viscosities is unknown and does not follow the expected logic (i.e a result 15w45 from the example in #1).

I was surprised to hear the exact same answer from two different oil company reps.


Ask those two reps why my engines live 250 and 300K doing blending at every OCI?
BTW.... when they enter the junkyard 17-18 years later, it's due to rust or blown transmission and the engine is always used again in another vehicle. Heck, the ones I send to the junkyard don;t even smoke or use more than quart of oil between changes.

Those two guys need to try it, prior to bad-mouthing it. My next concoction will be Formula Shell conventional mixed equally with Quaker State Synthetic.

 

[PeterPolyol]

It's very true, the result will often not follow linearly as logic might suggest. It's because of differing means of achieving viscosity modification are chemically different.

Based on what I've gathered, a simplistic hypothetical: one grade might employ PPD only while the other grade employs VII only. If you mix 50/50, the resultant treat rate of PPD may be only 30% as effective, while the VII treat might only be 35% as effective as they were in their original formula. That may in turn be the result of different ratios, viscosities and quality/Groups of the base blend

It really just means that with multigrade oils, you just can't be too sure about the viscosity change, not that anything will grenade as a result. I'd not even worry about equally qualified ILSAC products, they're rather predictable and largely compatible IMO, same brand or not.

 

[oil_film_movies]

Its right to be concerned about surface compatability (competition) between, say, some titanium, with some moly, maybe tungsten, antimony, different flavors of ZDDP, esters, detergents, etc. Mixing brands puts in a lot of unknown competition thats not proven to pass all the dexos1 Gen2 tests, 229.5, A40, whatever.

As for mixing base oils, I'm less concerned with mixing sets of PAO, GroupIII, GroupII, POE, all at different cSt's, although its possible that could go south I guess.

Great, read BITOG and start worrying about everything. OCD

 

[Ducked]

Originally Posted By: demarpaint
I've read that here many times before. While it's OK to mix, in the case of different grades the outcome is unknown. Still people think they're going to concoct some special viscosity. That's not the case though.


They'll concoct some special viscosity all right.

They just won't know what it is.

I mix straight 40 and 15W40. I don't know what that is either, but only one of the components has VIIs so the scope for serious synergy is probably somewhat cinched.

 

[oil_film_movies]

So the Widman viscosity mixer calculator is garbage? Base oils, with dispersants, are miscible, so it should be fine. KV100 at least.

 

[PimTac]

Originally Posted By: KevinP
Every time you change the oil you mix products.




Not if you are putting the same oil brand and grade back in.

 

[JohnnyJohnson]

Really then why don't they have a warning on their bottles?

 

[ZeeOSix]

Valvoline just says that because if they did recommend it then they have no idea or control of what the ending xW-yy viscosity is. I bet every oil maker will tell you the same thing.

 

[trooplewis]

Someone please clarify this discussion?

If I mix a 5w-30 synthetic with a 5w-20 synthetic, am I going to get a result that is higher than 30 or lower than 5 regardless of the proportion? Done this a couple times in one of my Hyundais. It would not be unusual to top off the 0w-40 in my old 2001 Benz with a 5w-30 as well, it's now going on 204k miles with no engine issues...

 

[passgas55]

So if I mix a 30 mono with a 40 mono at the 50/50 rate I would get a 35 weight.(a high 30 or a low 40 )

 

[OVERKILL]

Originally Posted By: oil_film_movies
So the Widman viscosity mixer calculator is garbage? Base oils, with dispersants, are miscible, so it should be fine. KV100 at least.


That's basically it, and Shannow, myself and others have covered it a few times. What's on the other side of the W is the potential problem, as it becomes an unknown. In a climate where that's not much of a concern, I'd wager there really isn't much risk.

On the other hand, the mystique some seem to ascribe to this practice, like they are performing some dark art, is ridiculous. The odds of mixing up something better than what's available fully formulated in a bottle for the application are so remote they aren't even worth considering.

 

[OVERKILL]

Originally Posted By: trooplewis
Someone please clarify this discussion?

If I mix a 5w-30 synthetic with a 5w-20 synthetic, am I going to get a result that is higher than 30 or lower than 5 regardless of the proportion? Done this a couple times in one of my Hyundais. It would not be unusual to top off the 0w-40 in my old 2001 Benz with a 5w-30 as well, it's now going on 204k miles with no engine issues...


You might up with a light 10w-30 or a heavy 10w-20, or maybe it keeps its W rating, but you wouldn't know without running the final product through CCS and MRV testing. Base oils with waxes in them do weird things at low temperatures, particularly when mixed and cycled. This isn't an issue with PAO, but generally two predominantly PAO-based lubes aren't what are being mixed. This may also be the case with POE's and AN's, but Tom NJ or Molakule would know better than I.