Seals

[MolaKule]

Good answers; keep 'emcoming!

 

[MolaKule]

All good answers.

Here are some more dynamic effects leading to radial lip seal leakage:

1. Thermal expansion and excessive heat
2. Cracking of the element,
3. Deterioration and degradation of the seal's compound,
4. Excessive softening or stiffening of the seal compound,
5. corrosion of the shaft
6. lubricant breakdown (sludge),
7. Seal fatigue,
8. Nicking and pitting,
9. Stickslip
10. Vibration,
11. Excessive eccentricity of shaft and/or seal interface
13. Case leakage (seal case).

 

[Titanium_Alloy]

MoleKule,
It seems like a seal started leaking in one my car. The seal is where a drive shaft connects to a rear differential. How long does a rear differential seal usually last (the car is 1996)? I'm running M1 75W-90. Do you think that switching to Redline might reduce the leak? How about running a heavier weight (like 75W-140 or 80W-90)? Do you know if AutoRX treatment will help?

Thank you,

 

[MolaKule]

It sounds as if your pinion drive seal is leaking. Try ARX first. If that doesn't stop the leak, then a new seal is in order.

Use Pennzoil 75W90 dino Gear Lube with the ARX.

 

[MolaKule]

MolaKule on, "Seal Conditioning and Swelling."

Seals are made by molding synthetic rubbers called elastomers.

Elastomers are made by mixing a filler material with a plasiticizer, the plasticizer being a high molecular weight ester or di-ester fluid.

Under the conditions of heat and the stress of oxidation and additives, such as dispersants, seals can degrade. Sludge buildup at the seal's interface is the number one cause of seal degradation.

Seal Degradation is:
1. Plasticizer loss or change in plasticizer,
2. dimensional change through chemical attack or mechanical wear,
3. hardening due to loss of fluid's swelling agents,
4. attack by sludge.

Seal swell results in the "increase" in the lateral dimensions of the seal. Usually, the "radial" dimension of the seal is decreased. One cannot "overswell" the seal or all sealing capabilites will be lost through mechanical wear. Also please remember that, "what goes up, must come down."

Seal conditioning is the cleaning or removal of unwanted sludge and the return of some of the seals plasticizer that may have been lost. Seal conditioning should not only clean the seal, but return the seal's "pliability." The exact mechnism of returning "some" of the pliability to a seal is due to a mechanism called diffusion.

Nothing, and I repeat nothing, can return a worn or used seal to it it's original dimension nor to its original pliability.

[ August 03, 2004, 02:40 PM: Message edited by: MolaKule ]

 

[MolaKule]

Seal Swell:

For automotive engines and transmissions, the targeted seal swell is generally around 12%, whether the base oil is mineral, majority PAO, PAO/ester, partial-synthetics, or high ester content fluids.

A test by the ASTM, ASTM 6546, will provide a better set of testing rules for up to 1,000 hours of testing at actual service temperatures.

Contrast this for aerospace hydraulic systems, where milspec MIL-H-5606, allowed an acceptable range of 18-30% seal swell volume. The seals used are ACN NBR's, or high-acrylonitrile seals of butadiene-acrylonitrile elastomers.

The latest MIL-H-87257 fluid has an operational range of -65 F to 375 F and is a high ester content fluid with low viscosity PAO oils, and is compatible with both NBR and fluorocarbon seals. The 18 to 30% seal swell spec is still allowed for these fluids.

 

[Jimbo]

quote:

---

Originally posted by MolaKule:
The answer is E and B in that order.

While esters can cause seal swelling by altering the plasticizer a bit, Dispersants not only can extract the plasticizer but also alter other material properties of the seal.

Dispersants containing high nitrogen content (such as amine-type or succinimide-type dispersants) have been implicated in causing seal damage to fluoroelastomer seals such as Viton. The low molecular weight and high polarity molecules in some dispersants can "diffuse" into the seal material and extract the plasticizer. [The plasticizer is that material which makes the seal pliable.]

---

I just ran accross an SAE paper about how much more aggressive toward floroelastomer seals ("Viton") the newest generation turbine oils such as Mobil Jet Oil 291 are compared to older turbine oils, like Mobil Jet Oil II.

While they are all ester-based, the newer fomulations contain amine-based antioxidants which are attacking seal elastomers.

Northwest Airlines, for one, seems to be reverting back to Mobil Jet Oil II, possibly because of seal failures.

The basic problem is that higher efficiency new engines run much hotter than in the late 1950's when these seal materials and ester-based turbine oils were invented. Temperatures of over 250C are now being seen. Seals are losing over 50 percent of compressive force in just 100 hours at 200C with the new oils.

 

[TallPaul]

Regarding the "myth" of switching an older car to synthetic and causing leaks, this link says leaks were due to a different seal material in older pre-1980 cars (see last paragraph): http://www.salemboysauto.com/faqs/default.asp?Action=Q&ID=42
Is this true? Then I would think we really don't have to worry about a 90s vehicle leaking when switching to synthetic. Furthermore, if synthetic caused leaks, why wouldn't a synthetic blend oil also cause leaks?

 

[MolaKule]

I disagree with him on two counts.

1. Synthetics are not thinner, they have the same viscosities as mineral oils, they just flow better.

2. I ran Amsoil and Mobil 1 in 1973 cars and on that had mineral oils in them before purchase and never had seal leaks after switching.

One thing for sure, if you had bad seals before switching, synthetics will show you the bad seals.

 

[MolaKule]

quote:

---

Seal and Fluid Test

I. Goal of Experiment:

Determine fluid effect on common fluorocarbon elastomer seal materials using two dissimilar synthetic base oils.

II. Materials Used and Test Protocol:

Pure, non-additized fluids were used in 250 mL quantities to cover seals and placed inside a 2-L beaker; one fluid was a 12 cSt Di-Ester, the other a 12 cSt Polyol Ester. Test duration was 45 days. Fluid temperature was brought up to 150 C for thirty minutes every other day, while air was pumped through hot oil using an Aquarium pump.

Seals were all new Flourocarbon elastomer seals from various seal manufacturers and included rear main engine seals for GM Chevy small block engine, input-pinion drive seals for Chevy 10-bolt differential, and axle seals for Chevy Suburban 4X4. Seals were cleaned with hexane after experiment, allowed to dry, and their weights re-measured on an electronic scale accurate to within 0.01 grams. A new set of seals was used for each fluid experiment.

III. Test Results

1. Di-Ester
A. Durometer - 5.3% (toward softness)
B. Flexibility – increased slightly
C. Peeling, cracking, or any other physical damage – none.
D. Dimensional change – + 7%; increase in lip height and decrease in radial dimension.
E. Wetting and Fluid cling – good.
F. Effects on Steel core – none; no rusting, no scale or discoloration.
G. Fluid Color and opacity change – showed a slight change in color toward a darker amber and a slight increase in cloudiness.
H. Weight Change – no detectable change.



2. Polyol Ester
A. Durometer – 3.7% softer after test.
B. Flexibility – increased slightly
C. Peeling, cracking, or any other physical damage – none.
D. Dimensional change – + 5.7%; increase in lip height and decrease in radial dimension
E. Wetting and Fluid cling – Excellent.
F. Effects on Steel core – none; no rusting, no scale or discoloration.
G. Fluid Color Change - ! No darkening and no change in transparency. No color shift.
H. Weight Change – no detectable change.


IV. Discussion Topics:


A. Durometer – Change in hardness or softness of material?

This measures an increase or decrease in the bulk hardness or softness of the material after soaking and temperature cycling.

From the results of this test (by no means totally scientific), we see that di-esters make a seal more soft than do polyol esters.

In our case, we used a spring loaded mechanical pressure guage that was lowered a specific distance to emulate a duromoter machine. The stiffness was measured before the experiment, and then afterwards. The softer the material, the more the pressure guage depressed into the material. The less the guage tip pressed into the material, the stiffer it was.


B. Flexibility – Did material increase or decrease in flexibility?

In our case, we used a spring loaded mechanical pressure guage to displace the lip edges a prescribed amount. We could not detect any changes down to 0.01 gram.

C. Peeling, cracking, or any other physical damage?

Some chemicals will cause the seal to peel, crack, or show some other damage during soaking and after washing. Neither of these fluids showed any physical damage as per above.

D. Dimensional change – A “+” represents seal swell while a “-“ represents seal shrinkage. A certain amount of seal swell allows for a tighter seal and reduces the potential of leakage. If the seal shrinks, you will have leaks. In Group IV majority formulations, one needs some kind of seal swell to balance out the slight shrinkage or “non-swelling” from PAO’s. I personally was NOT surprised at the results since other testing with various ester formulations of all types had not shown any real seal swell issues.


E. Wetting and Fluid cling – Subjective observation. Since the viscosities were almost equal, we timed how long it would take for oil to drip off the seals, and how well the fluid “wetted” the seals. All seals were well wetted but the polyol ester showed the best fluid cling.


F. Effects on Steel core/backing – rusting, scale, separation from elastomer, or discoloration? Since there were no anti-oxidant or
metal deactivator additives in the base oils, one might see slight oxidation of the core/backing. None was observed.


H. Fluid Color Change - ! Darkening and or change in color?

I considered this item to be a very important test item because a change in color or transparency meant that seal material might have migrated into the fluid, and or the fluid may have “diffused” into the seal material, displacing fluoroelastomer molecules. As seen in this test, the Polyol Ester was the most stable fluid. The di-ester showed very slight darkening, a slight increase in cloudiness, and a slight change in color toward a darker amber.

I. Weight Change – Measure weight to see if mass was gained or depleted. This is related to items “A” and “H.” Any mass gain of the seal might indicate fluid diffusion into the seal material.

V. Summary

While not an “official” scientific or ASTM test, the base oils tested showed remarkable stability. The seals showed only slight swelling.

The only thing we did not duplicate was localized heating due to shaft rotation as in actual axle or engine operation.

---

 

[bruce381]

I like it great test sound ASTM to me. did you also include any natural rubbers? that would make a dramatic
comparison.
bruce

 

[MolaKule]

Thanks Bruce.

Sorry, no natural rubbers since I wanted to see for myself if any of those commonly used synthetic fluids affected automotive-specific seals.

I am building a test fixture using our PCMO evaluation engine to drive a bearing and seal that will be immersed in the fluids mentioned to determine how localized heating and friction in the presence of the fluid (at the seal lips) affects them.

Of course, with the advent and introduction of Teflon and other advanced seal materials, seal swell may be a non-issue in the future.

 

[bruce381]

That is a much better test to me than a static soak test it sounds like an educational project as far as seal leakage, swell and wear are concerned good luck I hope it has good repeatablity. Even as seals get better and change in materials I still do see buna and natural rubbers used.
bruce

 

[MolaKule]

And if you or anyone else has anny seal swell experiemntal information you would like to share, then please do.

The literature on dynamic and even static seal swell is very sparse since the additive manufacturers of seal swell compounds, base fluid manufacturers, and seal makers don't release a lot of info on their tests.

For most motor oil tests, seal swell compound levels are determined experimentally.

 

[bruce381]

Kinda off subject but about 10 years ago I did some race car shock oil testing and had seal testing done on both swell and hardness buy Busak+Shamban Inc.
Fort Wayne IN 219-424-9631 This was a ASTM test as I remember. They did the testing since I think they made the seals to I do not remember though.
The shock oil I came up with had a VI of 526.

bruce

 

[unDummy]

Nyelubricants had seal compatibility charts in one of their tech papers. I can't find the 'paper' but here is a condensed chart.
http://www.nyelubricants.com/chart.htm#1

And, what page in Nissan's owners manual warns against using synthetics. I know Nissan recommends mineral oils, but unlike Mazda, doesn't warn against synthetic oil use. Being pro-mineral oil is not the same as being anti-synthetic.

The related links here also give the seal testing requirements for Dex and MV.
http://www.lubrizol.com/ReadyReference/DrivelineLubricants/14-atf/default.asp

 

[MolaKule]

Seal compatibility charts usually have a fluids verses seal-type table but usuall have no limits on seal swell/shrinkage.

 

[Rapidchaser]

Hi,
Brand new to the forum and quite ignorant when it comes to all the chemicals in todays oils (yesterdays too for that fact)
Some of these posts are a little disscurraging for me.
Let me explain! I just ordered 3 cases of Mobil 1 synthetic.
I am now using Pennzoil 40 in my Jet boat and have no leaks.
Do I need to change all the seals and gaskets in this 460 BBF in order to use the synthetic??
I sure as heck don't want the bildge full of oil

 

[kgb007stb]

We have a 1995 Pathfinder, those cars have solid engines, ours has 110k, 12 years later and absolutely no leaks what so ever. Before our uncle sold it to us he used nothing but dino, I have been running synthetics for the past 10k without any problems. Since we use this car hauling around the house and a spare backup, I may consider switching back to dino due to the low mileage that it sees.


I do read lots of comments that Frank made about seal pliability, just still confused when an engine is kept in a sound clean condition, will the synthetics somehow cause seals to be less pliable. Most synthetics today are Group III, so this is in the dino area, I did have a car that used synthetics PAO/ester based and it developed a minor leak at around the 140K mark. I got rid of the car before I found this web site, just wondering how dino oil would have worked.

 

[Kestas]

Our company (formerly known as Chicago Rawhide) produces seals, and I often interact with seal engineers. Here's a couple of things I learned from them to add to the discussion:

The bore or shaft finish has an important effect on the seal performance. If the ground finish has any axial component (angularity), this can result in an undesirable pumping action for the fluid.

Our company tests seals that we supply to the OEM only with the manufacturer specified fluid. We don't test using any "upgraded" fluids, such as Mobil 1 ATF or any other synthetic fluids, unless it is specified by the manufacturer. Since there haven't been any wholesale reports on this board about seals damaged by using upgraded fluids, I'd say we're safe to use them. I just thought I'd mention that we're on our own when we stray from OEM specified fluids.