The GM class actions allege that Dex-Cool used in certain 1996-2000 model year 4.3 liter vehicle coolant systems results in sludge, and, that the intake manifold gaskets (IMG) used in certain models and model year GM vehicles are incompatible with Dex-Cool.

The certified lawsuit breaks down the Class Members into two sub-classes:
1. All Class Members who purchased or leased a GM vehicle in Missouri with a 3.1, 3.4 or 3.8 liter engine that was factory-equipped with DEX-COOL, and,
2. All Class Members who purchased or leased a GM vehicle in Missouri with a 4.3 liter engine that was factory-equipped with DEX-COOL.
The sub-classes are named “Gasket Sub-Class” and “Sludge Sub-Class” respectively.

Evidence: DEX degrades the nylon IMG
The court said that all of the above had no bearing on whether it had represented a written warranty or unlawful practice. They appreciated more that the plaintiffs presented evidence that DEX degrades the nylon IMG within the class, no matter of its size or shape. Plus, GM was shown to have issued a TSB to its dealers calling for a replacement gasket made from different material. GM never disputed that DEX degrades the nylon 6/6 IMG.

Expert witness: DEX-IMG incompatibility well-known
One of the documents is from a 50-year veteran of the gasket and seal industries. A member of the SAE, ACS (American Chemical Society) and ASTM, the latter of which he served on the D15 coolant committee, he states that he was aware of GM’* 3.1 liter, etc, IMG failures well before learning of the lawsuit. He goes on to say that the gasket’* poor design and incompatibility with DEX was well-known in his industry. What brought up the discussions was GM’* adopting DEX in 1996, which of course led to widespread testing by him and peers. Those companies included heavy duty manufacturers Caterpillar, Cummins and International. He authored two technical papers, derived from thousands of hours of testing, focusing on the effects that DEX’* corrosion inhibitors have on rubber and plastic gaskets and seals, including GM’* IMGs in question. He concludes that the two are incompatible because DEX OAT inhibitors degrade both silicone and nylon, of which these gaskets are made.


For more specifics, the IMG is described as Nylon 6,6 carrier, 33% glass filled, injection molded, single silicone sealing bead. This man felt the IMG was not a good design to begin with, and then the inhibitors start attacking the weakened carrier. Evidently, because the silicone sealing bead is not molded over onto the carrier, the carrier is in direct contact with the DEX. Tie that in with no compression limiters, needed to maintain gasket integrity (see photo above), to begin with and that, according to the expert, is why the gasket is prone to fail.