Seals

[MolaKule]

We know that seals in an engine are used as a barrier to prevent leaking around rotating components.

Note: We are NOT discussing pan or valvecover gaskets, which may or may not be constructed of synthetic rubber (elastomer).

Let us assume we have a fully formulated oil complete with either a synthetic or mineral oil base and additives.

Which of the following components has the potential to attack seals and cause leakage if not properly formulated?

Please Priortize them as worst and not so bad.

Hint: Pick only two as there are only two real possibilities.


A. PAO Base oil

B. Ester Base oil

C. GI to GIII Mineral Oil Base

D. Viscosity Index Improver

E. Dispersant

F. Detergent

G. Rust Inhibitor

H. Oxidation Inhibitor

I. Metal Deactivator

J. Defoamant

K. AW/FM package.



[ March 21, 2004, 07:54 PM: Message edited by: MolaKule ]

 

[Primus]

A. PAO base oil
K. AW/FM package

 

[MolaKule]

Okay, this is a "tuffy" so I will rephrase the question and be more specific.

Which of the following components has the potential to diffuse into the seals, change the seal's properties, and cause leakage if not properly formulated?

Diffusion means to "spread into" from one source into another. Here, molecules from a component's source may spread into the seals and alter the seal's properties.


The answer may surpise you!

[ March 21, 2004, 09:46 PM: Message edited by: MolaKule ]

 

[Not the Autorx Frank]

wild guess
B and D

I'm so outta my leage in here..

 

[MolaKule]

NTAF,

Pretty good wild guess. One of your selections, B, is actually "not so bad," or number two on the list.

We can discount D, (Will explain later).

But keep trying!

[ March 21, 2004, 11:59 PM: Message edited by: MolaKule ]

 

[JoggingGuy]

My wild guess: B and A. One shrinks seals by itself, one swells seals by itself, both have to be present in the right amounts to be effective together

 

[JohnBrowning]

Well my guess is K and G.

 

[jason07-1zzfe]

1st- J
2nd- B

 

[1 FMF]

1st is (A) PAO - I thought all by itself it will cause seals to shrink. Am I right?

2nd (since you already said so) is (B) Ester. I was under the impression this will cause seals to swell, I guess meaning not so bad from a certain perspective. Am I right here?

For 2nd I was going to say Detergent, because they would most likely be the cause of deposits/sludge forming around seals to harden them up if not properly formulated.

[ March 24, 2004, 06:43 PM: Message edited by: 1 FMF ]

 

[MolaKule]

The answer is E and B in that order.

Seals can be damaged by mechanical abrasion, heat, and chemical attack. Sludge formation is the most prevalent form of seal degradation. But why sludge? Sludge contains high polarity and very small molecules such as amine molecules from various additives, most notably, the dispersants. (Microfine abrasion particles such as metals and silicon can damage them as well, but modern filtration usually removes most abrasion particles).

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.]

To mediate ("counteract") dispersant attack on seals, one can "post-treat" the dispersant with various reagents such as boric acid or epoxides.

So for any additive, one must fully test that additive to determine seal compatibility, and to determine how it behaves with other additives.

Since PAO molecules do not diffuse into seals, they do not swell or condition seals. In piston engines, seal swell volume needs to be 18-30% and can be provided by using various esters or aliphatic alcohols. One of those esters (not used as a base lubricating oil) is triphosphite esters in combination with hydrocarbonyl-substituted phenols.

If the base oil is a PAO/ester combination which contains certain percentages of lubricating esters, then seal swell additives are not needed.

[ March 24, 2004, 11:28 PM: Message edited by: MolaKule ]

 

[MolaKule]

The reason we can discount D is that the VII molecules are very large and thus would have trouble diffusing into the elastomer, and because most VII's are not amine or succinimide-based.

Now as mentioned in the QOTD thread regarding Viscosity Index Improvers, some VII's are dispersant VII's which serve two functions; one to improve the stability of the viscosity over wide temperature ranges, and to disperse sludge molecules. However, there is a different chemistry involved with dispersant-type VII's.

 

[jeepzj]

I've been using Amsoil 10W30 ATM in my Jeep. Should I be worried about seals in my engine with this oil? Thanks

 

[MolaKule]

No. I think the Amsoil ATM has had good seal compatibility history.

 

[MolaKule]

Another seal Question.

How does a Radial Lip Seal actually seal the sump oil, I.E., what is the mechanism by which a Radial Lip seal on a rotating shaft inhibits the oil from leaking to the outside?

 

[Motorbike]

That type seal is used in wheel bearing hubs and rotates on the sealing surface as opposed to say a crankshaft main seal which is in dynamic operation " spinning inside a fixed seal " and utilises a variety of gland widths per the makers choice of design.

These seals are conical and have a progressive type sealing area with a series of directional short rises that direct the lube back to where it tries to escape from with a final lip at the end . Most times upon inspection you find accumulated lube at this lip .

EDIT:

Actually most small trailer wheel bearing seals do not use the directional little risers* that help direct the lube back to where it belongs

* for lack of technical name

[ April 29, 2004, 08:12 AM: Message edited by: Motorbike ]

 

[dropitby]

I have a 94 Nissan 2.4 engine and its developed a leak and I think its the front seal. I've used 10/30 & 20/50 Castrol Syntec for the life or about 135000mi. It never used oil but would changing to dino oil like Chevron Delo 400 15/40 help!

 

[Frank D]

To Dropitby: My 96 1.6l Sentra had a front seal leak at approx 150,000 miles which I had repaired at a local shop and with part, labor & tax was $103, pretty inexpensive in this day. The mechanic said when it comes to a leak, nothing can replace a wrench and he said it was commom on Nissans. To Molacule: My new 2004 Altima 2.5l says in the owner's manual not to use synthetic. Is this due to a seal issue? The service dept at the dealer could not answer why.

[ April 29, 2004, 03:30 PM: Message edited by: Frank D ]

 

[MolaKule]

quote:

---

To Molacule: My new 2004 Altima 2.5l says in the owner's manual not to use synthetic. Is this due to a seal issue? The service dept at the dealer could not answer why.

---

Although somewhat off-question, I noticed the same thing in my new Pathfinder manual. Many calls to Nissan technical services did not answer the question.

I asked them about the SJ/SL oil requirements regarding seal compatibility what seals they used, and stated that many good synthetic oils meet this requirement, so is the main requirement for any and all SJ/SL oils or just for SJ/SL petroleum oils?
I also asked them why the non-synthetic statement and they couldn't answer.
They promised a written answer but I never received one.

Personally, I think they are full of it.

I curently use Mobil 1 10W30 with a proprietary add and have had good UOA's.

[ April 29, 2004, 04:53 PM: Message edited by: MolaKule ]

 

[MolaKule]

In addition to other Nissan inconsistencies, why would my 2001 Frontier allow synthetics to be used (as per the manual) but not my 2003 PathFinder. Makes no sense at all, and Nissan cannot give an educated answer it seems.

I think my next vehicle may be a Ford PSD diesel, since Nissan won't sell the Navaro over here.

 

[Shannow]

quote:

---

Personally, I think they are full of it.

---

That'd be Nissan when it comes to their "warranty specific" requirements for engine oils.