Shear and low temp viscosity

[hominid7]

We have all seen 10w30 and 5w30 oils shear down to a high 20 weight oil after a few thousand miles. We know this due to the viscosity @ 40*C and 100*C reported on used oil analysis. Im curious though, what effect does shear have on the viscosity at lower temps at which the 5w and 10w are measured? Does it stay the same, or go up or down?

If we have a 5w30 that shears down to a 5w20 after 3000 miles, that may not by itself have any great effect on engine wear. However if the 5w30 shears and becomes more like a SAE 20, that may have a much greater effect on wear, especially at start-up.

Any opinions or data?

 

[jstutz]

I think, and could very well be wrong, that the sheering comes from viscosity improvers that are added. So it seems to me that as they break down, the oil would start to approach the characteristic of the base oil. I dont "think" it would have an effect on cold weather, i really dont know though. will be interesting to get some more opinions.

 

[Jim Allen]

Yeah, the oil reverts to it's base and might flow a little better in cold weather. That might depend on how some of the other additives have fared, however. Those for cold weather performance.

 

[hominid7]

Thanks for the replies.... It would be interesting to see some cold weather testing on used oil to see just how it stands up.

Maybe i'll save a quart of used oil for the freezer test on my next oil change

 

[SpitfireS]

How much oil is needed to test the "W" rating?
I'm guessing the usual UOA sample isn't enough?
Is it possible to ask for a "W" rating test on used oil?

 

[Gary Allan]

Search around (email) and find out who has a cold crank simulator (CCS) or a mini rotary viscometer (MRV). I would not count on it being cheap if the tapered plug HT/HS test is any indicator.

That said, I don't think you lose much on the bottom end of things, but that's just my speculation.


Shearing isn't as common as it was in the past. Most oils are pretty shear stable at this point.

 

[SpitfireS]

Lets take the common conventional 10w30.
It starts at..? 11 cSt @ 100C?
Many used oil analysis after only 3k miles I've seen show those oils shear down to around 8.9 cSt.
(This is not about if this is a lot or not)
What "W" rating would these kind of oils have after 3k miles?

Can it be predicted using common sence?
Or an educated guesstimate?

 

[Gary Allan]

Quote:
Many used oil analysis after only 3k miles I've seen show those oils shear down to around 8.9 cSt.


Can you find some that don't also have a drop in flash point indicating some fuel component to the alleged shearing? I'd also grab the time span for used oil analysis done over such a short mileage span. Turbo's would also alter the view a bit, not always, but often enough.

Quote:
Can it be predicted using common sence?


I don't think it can be pondered using only those faculties ..we can navel gaze about it I suppose.

Quote:
Or an educated guesstimate?


Maybe someone educated will chime in.


Now for the novices input:

I've never heard of ppd degradation. I don't know if it exists. I don't know how big a role ppd's play in today's oils nor do I know what they're composed of.

 

[SpitfireS]

Originally Posted By: Gary Allan
Can you find some that don't also have a drop in flash point indicating some fuel component to the alleged shearing?

Point taken.
That said: wouldn't the fuel also make the cold oil less viscous aka thinner?
Quote:
I'd also grab the time span for used oil analysis done over such a short mileage span.

This I don't get, what do you mean?

Quote:
I don't think it can be pondered using only those faculties ..

Feel free to explore, find and use others.
Ha!
Quote:
we can navel gaze about it I suppose.

Where's Britney when you need her?

Quote:
I don't know how big a role ppd's play in today's oils

Not claming to not know as much as you don't know but this is why I asked.

How about: what could the difference in pp (not ppd

but maybe caused by ppd degradation ) degradation be between conventional and synthetic oils?
I'm still serious btw.