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Anatomy of a nylon LIM gasket

8347 Views 8 Replies 3 Participants Last post by  TechWannabe
For interest and curiosity, I took my failing LIM gasket and took some pictures. The first pictures are of the gasket after cleaning with water and a paper towel. The coolant port shows significant damage and was about to rupture causing a significant failure. Surprisingly, I was not any visible coolant, although I believe I was about to have a dead car.

Observations: no significant damage to the LIM around the dead ports,
Wood Antique

yet near failure at the flowing coolant ports.

Another website has already suggested that heat cannot be the reason for the failure because the dead port should be hotter than the flowing port as fresh cooled coolant would be flowing through the failed coolant port. It has been suggested on many sites that 2EHA is responsible for this failure because
a) non-Dexcool Series I 3800 motors did not show nearly the same failure rate with nylon gaskets
b) it has been suggested that the % 2EHA in the dead ports gets consumed as it is used to protect the neighbouring aluminum. Water and ethylene glycol are in large concentrations and not consumed. Both dead and flowing coolant parts are exposed to water and ethylene glycol, so these are unlikely to cause the failure.

I am going to see if I can infer how the damage progresses by looking at the various damaged points in more detail. It is definitely the nylon that fails.
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I removed the silicone gasket material from both coolant ports. The nylon had literally torn away and was being pulled towards the coolant ports. The only force I can see doing this is the contraction of coolant as the motor cools. It could also be pushed out by the nylon expanding if it has any ability to absorb coolant. However, I see no visible evidence of swelling that account for pushing the nylon out so far.

The nylon has clearly broken or torn.
Yellow Metal

The silicone gasket was still holding so I wasn't losing coolant. So far I cannot see any damage whatsoever to nylon of the dead port.
Automotive exterior Gas
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So far I have only found LIM gasket failure in a state where it has cracked through. Even this one which appears to be just beginning to crack, it is, in fact, right through.
Flowing LIM coolant port:

Dead LIM coolant port:

When compared to the dead coolant LIM port, the surface of the LIM appears very similar with the exception of the crack.

Flowing LIM coolant port close up. It seems to prefer to crack just at the bevel, which seems to be a physical weak point.
Yellow Close-up Wood Trunk Tree

Dead LIM coolant port close up:
Yellow Wood Close-up Metal
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I decided to compare the gasket channel of the coolant port to that of an intake port. To see the profile I will have to cut the gasket to get an end-on shot. For now...

Coolant port profile seems to have a slight bevel:
Water Metal

Another view of a coolant port profile:
Close-up Macro photography

Intake port seems to not have a bevel, but this could be an illusion.
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So far from my observations:
1) flowing coolant port has one apparently normal side, 3 failed sides
Yellow Metal

2) dead coolant port has 4 apparently normal sides
3) failures occur as a fairly neat crack along a predictable line (base of a bevel).

4) I did notice that the following site The potential role of DEX-COOL® (good information overall, and food for thought) compares a series I high milage non-Dex LIM nylon gasket with a Series II low mileage Dex gasket. The claim was made that the non-Dex gasket held up much better, and concluded that Dexcool was the cause. I don't have a high powered microscope available to me to see the nylon fibres, but I do notice that the gasket is constructed slightly differently. Notice that in the Series II gaskets a notch is put in the coolant port sidewalls. This notch doesn't exist in Series I gaskets. Although the construction of the Series I and II gaskets are different, it doesn't seem logical that the inclusion of a notch will cause gasket failure. I still agree that 2EHA is responsible. However, I am thinking that 2EHA is no the only factor.

First of all, 2EHA acts as a plasticizer during the making of plastics, not after a plastic is made. So, it's use as a plasticizer is not what is degrading the nylon in the gasket material. However, there does seem to be a relationship between 2EHA and the nylon-66 in the LIM gaskets.
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Great idea for a thread enslow, and nice pics of your gaskets coolant ports , I wish I could have gotten better pics of mine, but it was too brittle, and almost looked melted in areas, specifically the locating pins.
I did get a pic or two before I took it off.

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I really do not know enough yet to say whether I'd think heat, 2-EHA, or an improperly maintained coolant system, and by improperly maintained I mean not changing it soon enough, and or letting air get into the system, which would cause the dex cool to become more acidic.
I guess it could be a bit of all of the above, of course I do see that the nylon-66 gaskets were definitely not the best choice of material for the gasket.
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Here's some interesting, but very technical reading about polymers.


Now, although the acidic (-COOH) and amine (-NH2) chemical groups in nylon-66 break down in heat and acids, we can assume these chemical groups are stablized for the application used in automobile engines.

So, the question is now, does 2EHA have a role in removing or destroying the stabiliation of the COOH and NH2 groups? I think a lot of it depends on how nylon is stabilized. I'm sure that GM did not specify how the nylon is specified. They are probably using an industry standard of nylon-66 that is stable in water and heat. My current hypothesis is that once the stabilization of nylon-66 is compromized by 2EHA, the weakest area of the gasket (as shown in my pictures), heat weakens the nylon-66. Contraction of the cooling system then pulls the edges of the coolant gasket ports away from the rest of the frame and eventually the silicon gasket material falls off away from the sealing surface.

According to the current hypothesis, the degradation will have nothing to do with plasticization of plastics, but rather, a degradation of heat and water stabilzation processes allowing the heat and water to eventually break down the gasket. Dead ports will be susceptible to this too, but take longer to fail because 2EHA is not replenished frequently in this area of the LIM.

Now to test this hypothesis.
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Anyone want to grand me a few hundred thousand dollars to obtain the necessary analytical equipment to test my hypothesis? :D
I wish I saw this prior to trashing my old gakets
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