Yeah, I'd agree on that point. Another quick q though - why don't we see as much damage to the nylon carrier of the UIM gasket as we do to the LIM? I checked this morning, and yes, the UIM gasket carrier is the same material as the LIM gasket.

More food for thought.

The Silicone-rubber inserts are thicker. Are they mounted the same to the carrier? I can dissect both to see the difference. I'd say from EXTERNAL reference, the UIM gasket is manufactured a bit better in terms of sealing. The silicone-rubber portion is beefier, wider, and a cooler color.

You also have to take into account the thermal expansion coefficeints of the adjacent material. LIM gaskets are cast iron/aluminum interface, the UIM gasket is Nylon/Aluminum.

In other words, the UIM gasket thermal expansion coefficient is very closely matched to at least one of it'* adjacent materiels.

Fortunately, I'm an avid packrat. I still have that gasket hanging in my garage. The EGR bore is indeed crumbling. Here'* the pictures I just took 15 minutes ago:









Do you know what else I see in those pictures? A great reason for the UIM gasket redesign! The orange water passage sealing material seems to be pushing back into it'* flow channel over time. There is nylon supporting it all the way around, except for that channel (which is necessary for the material to flow through when it'* molded), and that is where those seals are looking to fail. With the push-in black gaskets on the newer UIM gasket, there is no such weak area. I'll bet that'* why that got changed.

Well, there is no reason I can think of that those reliefs would need to be there from a molding standpoint. If anything, it would just be an obstruction to material flow, and hinder the ejection of the part slightly.

Do we know if this gasket was two-shot molded, or if the sealing material was applied in a separate mold? There might be a way to tell by it'* injection point, but I don't deal with two-shot much at all.

Whatever the reason for their existence, I believe it'* an engineered-in feature of some sort. Perhaps it'* for expansion, as Bill suggested. I can't honestly think of any other reason for it.

Actually, expansion could account for the failure there, too. The area "gifted" with the molded in "expansion joint", is allowed to expand with heat, while the material directly next to it is not. That'* a recipe for stress and failure over time, isn't it?

I suspect that the area where the silicone (or whatever that is) overmolds onto the nylon is the thinnest part of the nylon carrier.

If the failure is caused by the "expansion slots" allowing some material to expand while the material next to it can not, then failure could be expected at the thinnest/weakest point. Without having a failed gasket in front of me, that kinda sounds like what we're seeing here.

Not to say that is the root cause of the failures, but it is one possible factor.

I would also be very interested in knowing if there is any difference in the thickness of the nylon carrier where the sealing material is overmolded, between a S1 and S2 nylon gasket. A small difference in thickness there could at least partially account for the different failure rate between S1 and S2 gaskets. Either take a micrometer to them, or look up a part print for each...?

Sorry for the double-post, but the last one was getting a tad long...

I forgot to mention that I picked up some small scrap parts from work. They're about 1" x 2" in size, made of nylon 66 (actually says >PA66< right on the back). It is not glass-filled, but I think that'* irrelevant as far as a reaction to chemicals. SO, if anyone wanted to do some scientific testing, and has the means to... I could pass those along.

I would have no problem doing the testing myself either, if we can agree on a solid, scientific method (and one that I can actually accommodate in my garage or basement).

EDIT: Also, this is interesting...

I think I may have found the company who makes at least a few of the Series II gaskets: http://www.spmgaskets.com/index.php?id=419