What makes HDEO more shear stabel than PCMO?

[Solarent]

Originally Posted By: Joe90_guy
I think what you said about PCMO & HDDO using the same high SSI VII (you can call it VM, it's the same stuff) might have been true in the past but not today.
The API CJ-4 HDDO specification contains the Kurt Oban 90 cycle shear test. XX-40 oils must stay in grade (ie, have a KV100 of 12.5 cst min) after 90 cycles of being mechanically sheared. This almost certainly means that the oils are formulated with shear stable 22 SSI OCP VII.


My post wasn't saying that HDDEO & PCMO use the same high SSI VII - I was saying that a lot of blenders use the same one for logistical reasons - that means they pick the one that gives them the performance they need for both categories and use that one. This was in response to the posts that HDDEO & PCMO use different ones with PCMO VII being less shear stable. In my experience blenders prefer to reduce complexity by choosing the VII that will perform well in both.

You are right that lower SSI OCP's are commonly chosen. Personally I don't really consider 25 SSI to be extremely shear stable - I often shy away from OCP's in general when going after shear stability in formulas. I prefer more complex molecules of the same molecular weight. (I would never use the Afton product that Shannow linked to)

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The other thing that you need to bear in mind is that HDDOs tend to contain more additive than PCMOs, particularly ashless dispersant to handle the soot you get in diesel engines. This tends to reduce the amount of VII you need which in turn reduces the tendency of the oil to shear.


I'm not sure where you are going with this, but you won't get any arguments from me on this point.

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If you're worried about shear on a motorcycle engine, where the engine and the gearbox share the same oil, them I might look for a specialised bike oil which carried some sort of API gear oil spec. Motorcycle oils aren't my thing so I can't recommend anything.


IMO specialized bike oil is the way to go - however I'd focus more on JASO spec vs API specs. They are a little more relevant to motorcycle engine design. Link for details on JASO Specifications

 

[Joe90_guy]

I do understand the arguments about component rationalisation but the reality of the US market is that PCMOs can't pass Sequence VIB/VID unless they use 50 SSI VII and HDDOs can't pass CJ-4 unless you use 22 SSI VII so you are forced to carry both types.

What do you consider low SSI? Sv 51? Sv 251? Never been a big fan if these VMs as their HTHS performance leaves a lot to be desired.

Does JASO contain a gearbox test? Just asking...only ever run the friction tests..

 

[Solarent]

Originally Posted By: Joe90_guy
I do understand the arguments about component rationalisation but the reality of the US market is that PCMOs can't pass Sequence VIB/VID unless they use 50 SSI VII and HDDOs can't pass CJ-4 unless you use 22 SSI VII so you are forced to carry both types.


We will have to agree to disagree on that point. I'm sure there are plenty of companies that use the same 25 SSI VII for both.

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Does JASO contain a gearbox test? Just asking...only ever run the friction tests..

Not that I am aware of, just the friction tests and the related API or ACEA tests (which is a baseline for the JASO spec - see the link I posted.)

 

[DWC28]

For those of you who like to do research, several years ago oil company C and P fought over "maximum protection against viscosity breakdown". Originally, as I recall, C claimed a viscosity index improver (VII) with higher shear stability index (SSI). They were comparing an SSI of 35 versus one of 50. C won that issue and P changed their advertising. Shortly after that C changed SSI to a higher number than P and the issue went to BBB again. This time C claimed that HTHS was the indicator of viscosity breakdown, not SSI. C won that time also. So now HTHS is the qualifier.

 

[Joe90_guy]

Interesting. I didn't know this story...

I love the US legal system. It seems to have been specifically designed for people to pick fights with other people over issues of absolutely no consequence whatsoever! It does however make the basis of some good telly programs like The Good Wife.

All I can say is that regardless of advertising & legal needs, the poor sod that has to design the oil in the first place has to meet every last requirement of the oil spec, even the stupid bits. Whether you use 35 or 50 SSI VII usually depends on what properties it imparts on the oil, and which, in the final analysis is the cheaper option. Simples..

 

[alarmguy]

Originally Posted By: bchannell
Assuming both are made from conventional base stocks, then what makes the HDEO any more shear stable than a PCMO? I read all the time where HDEO's are recommended because of their shear stability over PCMO.


I agree with Shannows explaination but will add my view.
Bottom line, an oil with a lower winter number will contain more index improvers then an oil with a higher winter number, that in itself will make the oil more shear resistant.
a 5w oil will have far more viscosity improvers then a 10w, a 10w far more then a 15w and 20w.

Its basic math. This improvers shear easy in a gearcase. So a 15 or 20w oil will hold up better then a 5 or 10 in a motorcycle shared sump. I dont care if its an HEDO or Automotive engine.

However I did do a LITTLE research just now, the API CJ4 standard does have specific test requirements for Cj4 oils regarding shear, I do not see any standards for automotive oil, but the link is below if anyone cares to compare some more. Its also looks like the Cj4 oils have tighter standards for cam wear, foaming, etc.

With all the above said, I dont care if its a s rated oil or c rated oil, a lower winter number will shear faster in a shared sump motorcycle. Ive done many UOAs in the past on my bikes, when using oils with lower w numbers, the higher (example 15w or 20) ALWAYS held viscosity best. Time and again, the same results on UOAs in shared sumps show the same results.

Here is the link, until this post I never cared to look at the actual test requirements for API and compare the SM and SN numbers against CJ4. After looking at them, I can see why in my new 14 Road King, if not using Harley oil, Harley requires a Diesel oil. Harleys do not have a shared sump but my previous bikes (all great bikes) were metric bikes with shared sumps.

API HEDO and Autmotive test requirements

 

[BrocLuno]

I'll bet the most shear stable HDEO will turn out to be Chevron SD Delo400 15W-30

That's the new'ish Severe duty oil

 

[alarmguy]

Originally Posted By: 901Memphis
People complain about Rotella T6 5w40 shearing in motorcycles


^^^ yes you are correct, when you have a wide spread like a 5/40 in a shared sump bike, it will shear rapidly and that is for any 5/40.

The thing is, the people who put the 5/40 oils in their bikes think they are smarter then the people who designed and built the engine, so they choose an oil weight that is not recommended, like the 5/40 thinking they are doing good for their engine.
Fact is, they would be better off sticking to the 10/40 or 20/50 oil weight recommended by the engine manufacturer with a sweet spot of 15/40 HEDO inbetween.

 

[TiredTrucker]

Originally Posted By: BrocLuno
I'll bet the most shear stable HDEO will turn out to be Chevron SD Delo400 15W-30

That's the new'ish Severe duty oil

Except that no one in the trucking arena is even talking about it nor have I seen it for sale at any truck stop, commercial truck dealership, commercial truck parts/supply outlets, etc. 10w30, now that gets talked about and is showing up more frequently. I know the 10w30 HDEO I get from Schaffer seems to be a little more shear stable on UOA's than the previous 15w40 Schaeffer I was using.

 

[HerrStig]

Originally Posted By: Joe90_guy
Interesting. I didn't know this story...

I love the US legal system. It seems to have been specifically designed for people to pick fights with other people over issues of absolutely no consequence whatsoever! It does however make the basis of some good telly programs like The Good Wife.

All I can say is that regardless of advertising & legal needs, the poor sod that has to design the oil in the first place has to meet every last requirement of the oil spec, even the stupid bits. Whether you use 35 or 50 SSI VII usually depends on what properties it imparts on the oil, and which, in the final analysis is the cheaper option. Simples..
The "BBB" is not the American legal system.