What are the driving characteristics of using too (1) low and (2) high of a viscosity ATF in an automatic transmission?

[SubieRubyRoo]

Viscosities lower with time, climate, and other factors anyways, so it's not even a correct answer, let alone relevant to my actual question.

Oils generally thicken with time in use when not diluted with contaminants, and that’s even ignoring any oxidative thickening that occurs from excessive temperatures when mixed with oxygen.

You’ll probably want to re-evaluate your methods using factual data.

 

[JasonATaylor]

bell_housing_torque is (engine rpm)/(rpm supplied to the rest of the transmission) as a function of ATF viscosity. Should be a straight line:

assuming the densities held fixed since that's basically close to how viscosity is measured. But, I don't know. It's why I am asking. I am not sure you realize I am asking for help, not posting answers.

valve_body_torque is the relative fractional change in wheel torque as a function of ATF viscosity during parts of a shift change due to valve body headers that dumkid is claiming matters.

By relative change, see https://www.beamng.com/threads/questions-about-torque-converter.77145/ where a similar question was apparently asked as I just now learned.

I

 

[JasonATaylor]

Oils generally thicken with time in use when not diluted with contaminants, and that’s even ignoring any oxidative thickening that occurs from excessive temperatures when mixed with oxygen.

You’ll probably want to re-evaluate your methods using factual data.

Perhaps but see

and it's not on topic to the Q anyways.

 

[MolaKule]

@JasonATaylor

RPM/RPM is simply some unitless number, not torque.

Definition of Torque Torque, specified with regard to the axis of rotation, is equal to the magnitude of the component of the force vector lying in the plane perpendicular to the axis, multiplied by the shortest distance between the axis and the direction of the force component. Regardless of its orientation in space, the force vector can always be located in a plane parallel to the axis. In the figure, the force vector F lies in the plane parallel to the line OL; the component FL, being parallel to OL, has no moment about OL, while the component FP, lying in the plane perpendicular to OL, has a moment, or torque, about OL equal to FP × d, in which d, the shortest distance between FP and OL, is the moment arm or lever arm. Torque is measured in newton metres in SI units.

"valve_body_torque is the relative fractional change in wheel torque as a function of ATF viscosity during parts of a shift change due to valve body headers that dumkid is claiming matters."

Valve Body headers - what are they?

Torque/viscosity = newton meters/(meters^2/s) = newton seconds/meter. What kind of unit of measurement is this?

Where are you getting this stuff?

The Mu(V) of AT fluids is a measurement of Dynamic friction; It is friction as a result of the relative rotational velocities of the clutches and fluid interacting with the porous clutch surfaces. I.e., It is the result of the fluids friction modifier chemistry with respect to the surface properties of the clutches.

 

[MolaKule]

Perhaps but see
View attachment 186966
and it's not on topic to the Q anyways.

No they don't, not anymore (since Dexron VI) with the modern shear stable Viscosity Index Improvers (VII's).

This is every bit pertinent to the discussion.

That was the major reason for the development of Dexron VI: shear stable VII's, a slightly lower viscosity for improved gas mileage, stable long-life friction modifiers, and better cold weather driveability.

There were the goals of Dexron VI and this was with Group II and Group III base oils. And today, with better base oils and improved additive packages, ATF's are even better.

 

[mdocod]

Oils generally thicken with time in use when not diluted with contaminants, and that’s even ignoring any oxidative thickening that occurs from excessive temperatures when mixed with oxygen.

You’ll probably want to re-evaluate your methods using factual data.

Oils can go both ways depending on the culmination of effects. The transmission in our H3 shears oil down. The transmission in our XC70 thickens oil up. Different conditions...

 

[MolaKule]

As an aside, HPL's "Blue" series of ATF's at 7.3 cSt, have all the same improved characteristics as Dexron VI but with a slightly higher viscosity.

 

[MolaKule]

Oils can go both ways depending on the culmination of effects. The transmission in our H3 shears oil down. The transmission in our XC70 thickens oil up. Different conditions...

And these were results from UOA's over approximately the same mileage as compared to the VOA's of the new oils?

 

[mdocod]

And these were results from UOA's over approximately the same mileage as compared to the VOA's of the new oils?

Caught me "red handed" (which is how I could feel the difference)... Well... Amber handed in the case of the H3

 

[MolaKule]

Caught me "red handed" (which is how I could feel the difference)... Well... Amber handed in the case of the H3

So the results of the UOA/VOA's correlated with shift feel?

 

[mdocod]

So the results of the UOA/VOA's correlated with shift feel?

Prior to draining the factory fill from the XC70, I seem to recall the shifting was excessively smooth (felt like borderline slippage)... I remember questioning whether a fluid change was going to create one of those conditions where the new clean fluid can't grab gears because the transmission was dependent on all the contaminants in the old fluid acting like friction material.

The factory fill fluid with 95K miles on it that flushed out of the XC70 was obviously thicker (and sparklier!) than anything sold as ATF new (also, it was basically black in color).

The factory fill was replaced with Maxlife ATF and the oil life program was reset. Shifting was immediately pretty snappy/harsh, more-so than I would have expected but didn't probe into it too much at the time I was just happy that the transmission was capable of a firm shift after a fresh fill of clean fluid. After awhile, the "learning" mechanism did soften up the shifting but never quite seemed "right" to me. I learned much later why the shifting seemed excessively harsh- fluid was too thin. Have had it on my radar to swap it out and finally did recently.

The factory fill on this XC70 is 3309- a bit heavier than Maxlife ATF and made from a conventional base stock that shears down initially then thickens up later. There are a handful of UOA's published for this type of fluid at various ages in Aisin transmissions around the interwebs that demonstrate this pattern and also prove that the "lifetime" factory fill claims are bogus for this fluid as it should actually be changed at 20-30K miles after the car is new to get all the assembly contaminants and initial break in wear debris out, then every 30-60K thereafter depending on how the car is used to prevent going down the thickening path with it. I thought this thinning then thickening pattern was commonly understood here at BITOG for many fluids?

The Maxlife came out of this transmission with about 50K miles on it a few weeks ago. The fluid that came out felt slightly thinner than the 3309 that we put in when compared at the same temps (which is what it is supposed to be), so I don't believe it thinned or thickened a meaningful amount in the last 50K miles, which makes sense, as its a more stable full synthetic fluid. Upon putting the 3309 in and resetting the transmission fluid life counter thingy in the confuser, the transmission now shifts better than at any point since we have owned the vehicle. Doesn't feel like slippage or excessively snappy/firm, right in the middle, just smooth but confident feeling shifts. Since this is conventional fluid I'll probably change it again in 30-40K miles or so. At that time I'm tempted to just put Redline D4 in it and leave it alone thereafter. I expect D4 would probably outlive the remaining life of that transmission anyway.

 

[MolaKule]

...The factory fill on this XC70 is 3309- a bit heavier than Maxlife ATF and made from a conventional base stock that shears down initially then thickens up later. There are a handful of UOA's published for this type of fluid at various ages in Aisin transmissions around the interwebs that demonstrate this pattern and also prove that the "lifetime" factory fill claims are bogus for this fluid as it should actually be changed at 20-30K miles after the car is new to get all the assembly contaminants and initial break in wear debris out, then every 30-60K thereafter depending on how the car is used to prevent going down the thickening path with it. I thought this thinning then thickening pattern was commonly understood here at BITOG for many fluids?

All very interesting and agree there is no such thing as a lifetime fluid.

However, I was referring to your own UOA's verses VOA's (not interweb results) on your equipment that you had personally done over similar mileages, and whether those results correlated with your observations.

 

[JasonATaylor]

No they don't, not anymore (since Dexron VI) with the modern shear stable Viscosity Index Improvers (VII's).

This is every bit pertinent to the discussion.

That was the major reason for the development of Dexron VI: shear stable VII's, a slightly lower viscosity for improved gas mileage, stable long-life friction modifiers, and better cold weather driveability.

There were the goals of Dexron VI and this was with Group II and Group III base oils. And today, with better base oils and improved additive packages, ATF's are even better.

I again disagree and I don't know what you insist on (a) fighting (b) here of all places; IMO Dexron VIs also shears down as the very high molecular weight molecules are thermally destroyed and otherwise broken down into smaller molecules. Here's an measured example contradicting you of it going from 6+-1 cSt down to 5.6 cSt after 43k miles. https://bobistheoilguy.com/forums/threads/dexron-vi-43k-miles-on-fluid-6l80e.354573/ Yes, if oil is used long past when it absolutely needs to be replaced, it should oxidize and turn into a new product, a solid gel full of oxidized carbon called sludge, but if the user is at all diligent, this side of the curve should never be experienced, so for all practical purposes (at least for most users reading this site), the viscosity should go down with miles, not up, for all Dexrons.

"This is every bit pertinent to the discussion." OK but I had thought the purpose of this thread was to know how shifting feels as a function of ceteris paribus ATF viscosity (meaning that only viscosity is being changed and all other things like friction modifiers, oil oxidation, color of the oil, etc., are exactly the same). There are a million threads on the net about peoples' favorite ATF shaggy dog stories, but I was hoping to have one by smart ppl just about this and nothing more. But, what would I know.

 

[kschachn]

Well, it all depends upon how you look at it. Using a thinner oil in a machine is always 100% compatible if your real goal is to get it into a yard. And it will get you to where you need to go until it fails and you need to purchase a new unit. Sales are inverse of longevities.

You have no proof that’s correct. I’ve used DEXRON-VI type fluids for many miles in my old Sienna and many miles before that in my old BMW. It’s fine to have opinions about things but I would suggest you not present them as facts unless you can back it up. DEXRON-VI is superior to the previous licenses in every way.

 

[kschachn]

I again disagree and I don't know what you insist on (a) fighting (b) here of all places; IMO Dexron VIs also shears down as the very high molecular weight molecules are thermally destroyed and otherwise broken down into smaller molecules. Here's an measured example contradicting you of it going from 6+-1 cSt down to 5.6 cSt after 43k miles. https://bobistheoilguy.com/forums/threads/dexron-vi-43k-miles-on-fluid-6l80e.354573/ Yes, if oil is used long past when it absolutely needs to be replaced, it should oxidize and turn into a new product, a solid gel full of oxidized carbon called sludge, but if the user is at all diligent, this side of the curve should never be experienced, so for all practical purposes (at least for most users reading this site), the viscosity should go down with miles, not up, for all Dexrons.

"This is every bit pertinent to the discussion." OK but I had thought the purpose of this thread was to know how shifting feels as a function of ceteris paribus ATF viscosity (meaning that only viscosity is being changed and all other things like friction modifiers, oil oxidation, color of the oil, etc., are exactly the same). There are a million threads on the net about peoples' favorite ATF shaggy dog stories, but I was hoping to have one by smart ppl just about this and nothing more. But, what would I know.

Which “very high molecular weight molecules” are you talking about? The base oil does not shear. Even so, it’s not a thermal process that causes shear in the viscosity modifiers. Oxidation causes thickening.

 

[JasonATaylor]

Which “very high molecular weight molecules” are you talking about? The base oil does not shear. Even so, it’s not a thermal process that causes shear in the viscosity modifiers. Oxidation causes thickening.

Ok let's assume you are right and ATFs shear up instead of down. Fine. Now the viscosity increases as you drive, so you might experience a change in the way the shifts happen. It might be better. Might be worse than what you prefer.

Now you can see the value of the thread, because you might not like the way it is shifting and by getting either a higher or lower viscosity ATF fluid, you might be able to either increase or decrease jerkiness to your liking. So, the usual way this thread is killed (saying it is dumb because you should just get OEM fluid already, duh) is wrong since you might not prefer OEM shifting, which itself isn't one thing but a changing thing since (at least) the viscosity changes as a function of miles/time.

 

[kschachn]

Ok let's assume you are right and ATFs shear up instead of down. Fine. Now the viscosity increases as you drive, so you might experience a change in the way the shifts happen. It might be better. Might be worse than what you prefer.

Now you can see the value of the thread, because you might not like the way it is shifting and by getting either a higher or lower viscosity ATF fluid, you might be able to either increase or decrease jerkiness to your liking. So, the usual way this thread is killed (saying it is dumb because you should just get OEM fluid already, duh) is wrong since you might not prefer OEM shifting, which itself isn't one thing but a changing thing since (at least) the viscosity changes as a function of miles/time.

What? I never said the fluid shears up, that’s nonsensical. Any thickening of the fluid is due to a phenomenon other than mechanical shear. I was also noting that the base oil molecules do not shear only the VM.

All DEXRON license requirements allow for shear. It’s that the prior specifications allowed for more than is allowed for in DEXRON-VI. So as I noted, DEXRON-VI is a superior fluid in every respect. That’s all I was really saying. Not just viscosity stability but oxidation as well.

 

[Pablo]

In practical terms within say 4-7 cSt at 100°C ATF - any transmission should not exhibit a drastic, or even noticeable difference in shifting pattern or feel at most shirt sleeve temperatures (~32-100°F) for most average drivers.

Maybe at 0°F it's possible that a lay person might feel a difference, but the car is going, it's cold, so no issue.

 

[SubieRubyRoo]

. So, the usual way this thread is killed (saying it is dumb because you should just get OEM fluid already, duh) is wrong since you might not prefer OEM shifting, which itself isn't one thing but a changing thing since (at least) the viscosity changes as a function of miles/time.

This is the reason for certifications and specifications. Barring external contamination, any fluid that has say, Dexron VI certification should have nearly identical shifting characteristics. Same with all the other fluids. That’s why there are specifications, standard additive packs, and base oil restrictions.

 

[MolaKule]

I again disagree and I don't know what you insist on (a) fighting (b) here of all places; IMO Dexron VIs also shears down as the very high molecular weight molecules are thermally destroyed and otherwise broken down into smaller molecules. Here's an measured example contradicting you of it going from 6+-1 cSt down to 5.6 cSt after 43k miles. https://bobistheoilguy.com/forums/threads/dexron-vi-43k-miles-on-fluid-6l80e.354573/

Better look again and assuming it is the same fill, the viscosity dropped 0.1 cSt, almost non-perceptible and within the test instrument's margin of error. In other words, it is in the "NOISE."

Did you read my comments in the next post after the analysis?

very high molecular weight molecules are thermally destroyed and otherwise broken down into smaller molecules

If you are referring to the Viscosity Index Improvers (VII's) then please state them as such.

I didn't know anyone was fighting. I thought we were discussing the technical aspects of ATF verses viscosity.

BTW, I still formulate both Manual and Automatic transmission fluids so I find these type of threads interesting.

Yes, if oil is used long past when it absolutely needs to be replaced, it should oxidize and turn into a new product, a solid gel full of oxidized carbon called sludge, but if the user is at all diligent, this side of the curve should never be experienced, so for all practical purposes (at least for most users reading this site), the viscosity should go down with miles, not up, for all Dexrons.

Something you need to know about the shear-stable VII's we use in modern ATF's. Shear- stable means they tend to resist mechanical shear but a major number of the VII molecules that have sheared will tend to reattach themselves after shear.

the viscosity should go down with miles not up, for all Dexrons.

Not, not for ALL Dexron type fluids. Modern ATF's starting with Dexron VI will go up in viscosity as the anti-oxidant chemistry is used up and dissipated.

"This is every bit pertinent to the discussion." OK but I had thought the purpose of this thread was to know how shifting feels as a function of ceteris paribus ATF viscosity (meaning that only viscosity is being changed and all other things like friction modifiers, oil oxidation, color of the oil, etc., are exactly the same). There are a million threads on the net about peoples' favorite ATF shaggy dog stories, but I was hoping to have one by smart ppl just about this and nothing more. But, what would I know.

If you don't want a sentence to be commented upon then don't it include in your responses; simple as that.

It's ok to be sarcastic but what we attempt to do here is to deal in facts, so calm down, you might learn something.