Auto Service World
Feature   July 1, 2006   by Andrew Ross

A Fate Sealed

How Factors Conspired to Create GM's Intake Manifold Gasket Troubles


If General Motors had been able to keep its intake manifold gaskets as tightly sealed as the lips of its suppliers and their competitors, there wouldn’t have been any problem whatsoever. Nonetheless, a few facts are clear.

For those in the industry, any doubt about the importance of reliable engine sealing must surely have evaporated with the recent announcement that class action lawsuits against GM in Canada and in the U.S. were likely to go ahead.

At the centre of the suits is the contention that the intake manifold gaskets on a number of GM engines were defective. And, by implication, that GM knew it but failed to inform customers.

The force behind the case in Canada is Winnipeg native Nigel Turl, whose $1.2 billion lawsuit alleges that GM installed defective gaskets on some 400,000 cars sold in Canada. Similar suits have also been filed in Ontario and Quebec. Lawyers have also announced the commencement of further class actions against General Motors of Canada Limited and General Motors Corporation in B.C., Alberta, and Nova Scotia.

Claims are that General Motors designed, marketed, tested and manufactured, in the 1995-2004 model years, various Buick, Chevrolet, Oldsmobile and Pontiac vehicles with a 3.1, 3.4, 3.8 or 4.3 litre engine, using a defective intake manifold gasket.

This contentious issue has been percolating for years.

Even the lawyers admit that it is too early at this stage to quantify the claims of the potential class members, but what is clear is that it is GM’s use of a “defective gasket” that is the focus of the moves in Canada.

In the U.S., the focus has been on the coolant rather than the gasket.

Those U.S. suits connect the failures to GM’s use of Dex-Cool, a coolant it first introduced in its vehicles in 1995 and sold in more than 35 million cars and trucks between 1995 and 2004. The coolant uses a long-life formulation that differs fundamentally from the familiar green coolant to which most vehicle owners are accustomed. In the U.S., more than a dozen federal and state lawsuits seeking class-action status have been filed against GM over a variety of engine problems that state a link with the use of the coolant.

The official position of Chevron Texaco, one of the suppliers of the GM specified formulation, is simply that no link exists. “The Dex-Cool line of coolants, licensed by General Motors to multiple coolant manufacturers for its GM 6277M specification, is not involved in the failure mechanism of the GM intake manifold gasket issue. GM thoroughly investigated these allegations and concluded the coolant was not at fault. Chevron’s own review concurs with GM’s findings. GM continues to fill all of its new vehicles with Dex-Cool.”

Accordingly, the opinion of one source was that the substitution of conventional coolant would do little if anything to prolong the life of the gasket.

Customers have complained of problems that range from small coolant leaks to complete radiator and engine failure. Court documents show that GM has received tens of thousands of repair requests related to Dex-Cool and engine gaskets in the affected models, and has considered recalls for some models.

The company has issued several technical bulletins to its dealers about cooling-related problems in its engines, but says it prefers to handle customer complaints on a case-by-case basis.

Causes floated on public forums include “stop-leak” pellets added at the factory, contamination with air from system leaks (Dex-Cool can apparently degrade and become acidic when exposed to excess oxygen), and improper service that involved adding non-Dex-Cool coolant or tap water to the cooling system.

Whatever the cause, one of the key points is what the expected life of such a part should be. In most, if not all cases in question, the gaskets did not fail during the warranty period. While many expect that such a part should last well beyond the warranty period, expectation is not the same as liability.

Regardless, the most credible explanation for the failure is more complicated than either lawyers or those defending the original gaskets have offered. While there is still much room for clarification and a full engineering study that may or may never come, it appears that the failure has many facets to it.

First, it should be noted that the construction of the original gasket was a plastic carrier with a silicone sealing bead system.

According to information from engineering sources that wished not to be named for fear of reprisals, at least part of the problem exists with the original material. While plastic carriers aren’t bad, the particular plastic chosen was not quite right for life alongside the Organic Acid Technology (OAT) of Dex-Cool. This plastic, part of the nylon family, has a tendency to become hard and crack in an acidic environment.

But that’s not the end of it.

In addition, the silicone used as a sealing bead is not quite right for the job, either. Sources say that it is not compatible with the fuel-air mixture or OAT coolant, particularly when that coolant has itself become degraded and more aggressive than the original chemistry might have been.

The cracking that is so prevalent on the failed gaskets is a result of the embrittling of the carrier combined with the swelling of the silicone bead in the presence of the coolant and/or the fuel-air mixture. The swelling puts pressure on the carrier and, because it has been weakened, it fails.

That is the short story. To really understand how this came to pass requires a little history lesson.

More than two decades ago, cork rubber gaskets were the status quo for sealing everything from valve covers to oil pans. Then rubber valve cover gaskets, and silicone, were employed. That allowed for greater variation in clearances.

Silicone sealed well and it was inexpensive. Fibre gaskets, by comparison, were tough to engineer around because they weren’t uniform, densities could vary, and fibres could vary. If there is anything that engineers love, it is predictability, and silicone gave them that as well as the ability to seal relatively large gaps due to its compliance.

Having said all this, it is very important to mention that the same materials and construction were used for certain Ford gaskets and, according to sources, those suffered one- tenth the failures of the GM gasket. So there is more at work here.

It is important to remember that the majority of engines suffering from gasket failures are the latest incarnations of some very old engines. The 3.1 and 3.4 engines are based on OE castings that started out as the 2.8 litre engine of circa 1979.

Those engines were quite simply not designed or built with the tight tolerances the industry has come to expect from today’s newer powerplants. The fact is that this may have played as much of a role in the gasket failure as either the gasket materials or the coolant.

Enter two phenomena. One is called tolerance stackup. Let’s say you are manufacturing two parts that are intended to be bolted together. If your tolerance is plus or minus three thousandths of an inch, but one part is at the minus three thou (0.003 in.) end of the scale while the other is at the plus end, you have an assembly that is well outside the generally expected norm.

Core shift, on the other hand, is when the various parts of a component may be of the correct dimension, but oriented differently laterally.

For example, Part A is supposed to have its boltholes and locating pins within three-thousandths of an inch of the ideal specification. Part B that it attaches to is also supposed to be produced within three thou.

The difficulty is that when you have one part out three thou in one direction while the other is out three thou in the opposite direction, you now have six thou of mislocation. If that mislocation is on an intake manifold to cylinder head mating surface, you end up exposing gasket materials directly into the flow of air-fuel, coolant, or motor oil.

Apparently, on the engines in question, you can actually have up to three millimetres of mismatch, which allows for barely any sealing surface to be squeezed between the flanges, in a situation where sealing is difficult at the best of times.

The result is that with only a little degradation of the sealing ability of the part, leaks result. And, apparently, lawsuits.

It is also key to note that due to a variety of factors, changing the coolant to a more conventional type would not be expected to extend the life of the original gasket materials much beyond that experienced in the field with the factory fill.

The solution, now in place at both the OE level and a number of aftermarket suppliers, is to use different materials that are better able to withstand the conditions. Back in 2004, GM already noted several changes to its sealing technology, and not just for intake manifold gaskets.

That year, the 3800 Series II, which is bearing the brunt of many of the complaints, reaped the benefits of the improved sealing technology developed for 3800 Series III engines.

Improvements on the 3800 Series II engine, for example, started with the rocker cover and oil pan gaskets, which were manufactured from an enhanced elastomer. The new gaskets provided better bead sealing and were more resistant to oil seepage for the life of the engine. The rocker cover gaskets were designed to enhance the structural rigidity of the covers, thereby reducing overall engine vibration.

Other gaskets were optimized with the same attention to detail. The throttle body gasket was manufactured of a new HNBR material, which is more resistant than the previous silicone material to long-term deterioration with exposure to engine coolant. HNBR is widely known for its physical strength and retention of properties after long-term exposure to heat, oil, and chemicals.

The intake manifold gasket used the same material at the coolant ports. The lower intake gaskets are made of HNBR, and were equipped with compression limiters that maintain appropriate gasket compression for the life of the engine.

Aftermarket gaskets followed suit to compensate for prior weak points by using materials and designs to prolong their leak-free life.

Key to the materials puzzle is the use of FKM material. This class of materials is sold under a number of brand names, perhaps the most familiar being Viton, which has been used on valve stem seals for years.

In addition, the use of torque limiters to the gasket carrier should help alleviate the crushing that was clearly evident in many failures.

While the outcome of the legal procedures is likely more than a year away, the solutions to the immediate problem are available today in the aftermarket.

And that is something worth talking about.

The Legal Question

Lawsuits surrounding the failure of the intake manifold gasket revolve around the question of the part’s reasonable life expectancy.

Lemon-Aid publisher Phil Edmonston says that a precedent for this expectation was set with the Ford 3.8 head gasket issue. That gasket was prone to failure, and Ford eventually relented under pressure to provide some relief by extending the warranty period to upwards of 100,000 km.

Lawyers handling the proposed class action suit in Ontario are more circumspect than that, stating that these are all issues that need to be determined when the case goes to court.

One such example arose during a public information event held at AML Motors in Toronto. That event was attended by John and Laura Desroches, owners of a 2000 Chevrolet Venture. The couple experienced problems with their vehicle in May 2004. Those problems eventually stranded the vehicle in Perth, Ont., where repairs were executed by independent service provider D-Tech Automotive.

The following is a chart of the occasions the van was in the shop and the work done.

November 27, 2001: 34,132 km. Coolant leak. Replace distributor shaft seal.

April 19, 2002: 40,296 km. Antifreeze leak. Replace bypass seal and top centre roller out of round.

January 17, 2003: 54,447 km. Transmission fuel leak. Replace clamp/hose pipe.

February 17, 2003: 55,391 km. Coolant leak. Loss at upper and lower intake manifolds; replace gaskets, clean all parts, remove oil pump drive, seal, gaskets and all fluids necessary.

March 21, 2003: 56,612. Coolant leak. Re-tighten hose.

December 4, 2003: 69,441 km. Antifreeze leak. No coolant leak found. Found oil leak to oil filter. Did lube, oil and filter.

Ms Desroches adds that much of the work done on the first visit at 34,132 km is the same as that done at 55,391 km (same gasket and seal part numbers). She says too that while she understands the questions regarding when the warranty or extension of warranty ends on the part of GM, “If they’ve already done this work, and in my case twice, and the vehicle still breaks down, there is certainly a problem that should be addressed by them.”


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