The potential role of DEX-COOLŪ in GM 3800 lower intake manifold gasket failures

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    Before you read further, let me introduce myself.  I'm not an automotive specialist or professional.  I'm an enthusiast, or hobbyist.  My interests are primarily focused on the Buick 3800 V6's commonly found in Pontiac Bonnevilles, various Buicks, Chevrolets, and Oldsmobiles.  I'm also an Administrator on, an internet Forum for Pontiac Bonneville owners.  Over the 6+ years I've been there and the forum it replaced, we have endured countless topics, gasket failures, and blown engines.  Our Gearheads on the forum have diligently fought the battles and we've learned a lot about how to help prevent the problems, but never really FULLY understood the root cause.  I, among others, have spent countless hours reading on the internet about all the lawsuits, reports, claims, and rumors.  I decided to take it a step further using some good analytical approaches, and some nice tools available to me at work.  I design and build custom research and development laser systems for Hewlett Packard.


    This page is primarily focused on the failure of lower intake manifold gaskets in GM 3800 motors.  These are pushrod V6 engines with cast iron blocks and cylinder heads.  The motors are renowned for being 'bullet-proof'.  Some are supercharged from the factory, and many are pushed to the limits of performance by other enthusiasts.  While other GM engines have had the same problems, I'm only going to briefly touch on them in this report.  I've long suspected DEX as being the primary culprit in early lower intake manifold (LIM) gasket failures, but to this date, nobody has proven it.  I won't prove it in this report either, but the grim reaper may be pointing a little more emphatically in that direction by the time he finishes reading this.



    The goals of this report are simple:

1.  To attempt to dispel the rumors about some of the possible causes of early gasket failure in these engines.

2.  To attempt to reveal all the possible variables that may play a role in these failures.

3.  To invite yet more controversy and discussion on the topic, and perhaps encourage someone to investigate further.


The investigation starts

    I have 2 sets of gaskets to compare that are good candidates for this report.  The first set was removed from one of my own cars, a 1995 Pontiac Bonneville SE, with the supercharged engine as a factory option.  The gaskets are OEM as installed from the factory and were removed at 125,000 miles as routine maintenance, the car was not originally 'equipped' with DEX (had the old-school green glycol stuff), and to the best of my knowledge never slurped the DEX at any time in it's life (the original owner's son-in-law is a Service Manager at a GM dealer, and knows better.....I bought the car from them).  The second set is from a 1998 Pontiac Bonneville SE, and these gaskets were installed sometime after 2002 when the upper intake manifold was replaced due to a presumed failure.  The UIM has a manufacturer's date of 2002, and the Gaskets were manufactured in 2001.  30k to 40k are the estimated number of miles that these gaskets were in the car.  It's unknown if the car had a coolant flush at the time of gasket and UIM install, but it is presumed (the work happened at a dealer, and GM dealers know about DEX's ability to turn acidic over time).

    Both gaskets are known to be made of the same materials.  The main carrier is Nylon66.  It was invented in 1935 by an organic chemist named Wallace Carothers who worked for DuPont.  The strength and durability of the material is more a matter of HOW it is processed than what it actually is made of.  Liquid polymers are blown through very small nozzles, and allowed to solidify, creating a very strong inter-woven mesh of fibers thinner than a human hair.  This is very important, and will be explained later in this page.  His patent was granted in 1937, and a short time later, depression caused him to commit suicide by drinking cyanide.  Ironic to say the least, but he had no clue what role General Motors would play in this story years later.  More information on Nylon can be found here.

    These two sets of gaskets were chosen because they represent the 'norm' in lower intake manifold gaskets in GM 3800 engines.  Series 1 gaskets tend to last much longer than Series 2 gaskets, and the transition year between these two engines were within one year of the introduction of DEX.  An important note to be made is that there ARE exceptions to this 'norm', but we'll address that later in the page.   

Basic Properties of Nylon66

    Nylon66 melts at temperatures from 255 to 265 degrees C, or 491 to 509 degrees F.  This is important, so remember it.  Tensile strength is 13,700psi, and even higher in 50% humidity, at 17,000psi.  This is also important.  Yet another property we'll care about later is it's elongation at the break point.  This is described in simple terms how much it stretches before it breaks.  Dry rating is 15-80%, and at 50% humidity, it runs 150-300% (at the break when stressed).  This might be important information in an application where it's subjected to water.  Nylon 66 Properties

    Nylon66's acid resistance is a more difficult story.  It boils down to what kind of acid we're talking about.  As shown on this page, Nylon66 isn't shown in the 'Acid Resistant' column.  While it resists SOME acids, it's not considered 'acid resistant'.  Taken from here, the data shows the resistance properties of Nylon66 to several common acids is poor.  We'll talk about that later.  In the meantime, try this link out for a backup of the acid resistance properties.

    We're concentrating for now on Nylon66 as the carrier (main frame of the gasket) rather than the silicone-based rubber tracings of the gasket, as it's very obvious in a failed gasket that the Nylon, for whatever reason, just plain 'let go'.

Properties of DEX-cool

    This page has a really good description of what DEX really is.  DEX uses OAT, or organic acid technology to extend the service life of the product.  But one of the primary ingredients is known to soften plastics (or polymers.......sound familiar?) if not kept 'in balance'.  One of these 'imbalances' is air introduced into the system.  This is typically from very small leaks in the cooling system that most car owners wouldn't be aware of.  These leaks, or any other failures, cause DEX to turn acidic over time.  Properly maintained, in a perfect or near-perfect system, this SHOULD never happen.  This is why we see some cases of DEX'ed LIM gaskets achieving longer lifetimes.  They lived in a perfect world.  Unfortunately, most of our cars aren't nearly as perfect under the hood as most of us would like to believe.

Let's get down to it

    Let's meet the victims:

On the left is the DEX 30-40k LIM gaskets....................................................On the right, the 125k non-DEX gaskets

    From this picture, we can all see that something just isn't right with the gaskets on the left.  But it's pretty typical.  Let's take a closer look.  We'll call them DEX and NON-DEX from now on.






Overlaid showing low-mileage DEX on the left, and high-mileage NON-DEX on the right:


    It's probably safe to say that for the purposes of this comparison, there's no reason to look any closer at the NON-DEX gaskets, but we will briefly do so later.  You can be assured that the problems we find here with the DEX gaskets do not even remotely exist in the NON-DEX gaskets in this comparison.  Again, there are exceptions out there, but they are isolated instances.  DEX-exposed gaskets typically start showing problems at about 30-50k miles, and NON-DEX at 100-125k miles.  Keep in mind, the gaskets on my OTHER Bonneville (1993 SSEi) looked just as good as these NON-DEX gaskets out of my SE at 85,000 miles.

    So off to the microscope I went, but I'd already seen what I was after.  The DEX gasket had some interesting characteristics.  I'd already concluded this some months earlier:


    This was about 6 months ago, before I really started digging into the root causes and the effects of the 'environment' on certain type of materials in question.  It looks pretty obvious that the DEX coolant wicked around in the path I showed in the picture above, but we still have to rule out over-torquing the gaskets, and the effects of heat.  For now, let's get on to looking even closer at the failed DEX gaskets.

    This is a 50x magnification (Nikon microscope with 50x objective lens and incandescent top-lighting) view of the INSIDE face of the coolant port that normally flows coolant (the other port is 'blind' and while exposed to DEX, doesn't actually flow):

    See the exposed fibers?  This isn't normal Nylon66.  It's been altered by something.  The NON-DEX gasket didn't look anything like this under high magnification.  Let's look at a lower-magnification view and I'll explain more.


    This is a 5X magnification view of the same coolant port.  This is shot from the 'LIM view', as if the camera were placed in the lifter valley instead of the lower intake manifold, and the picture was taken looking towards the gasket with the cylinder head behind it:

Coolant port..............eroded Nylon66.......................non-eroded Nylon66..............silicone seal


    Notice the eroded portion showing exposed fibers?  This is the portion of the Nylon66 gasket that is exposed to the DEX flow path through the gasket port, manifold, and engine.  The other port wasn't as bad.  Let's call it half as much fiber exposure.  But the other port is BLIND.  It has no flow.  The NON-DEX gasket under the same magnification looks like the non-eroded portion of the picture above (vertical band under the '1' of '1/1000').  Why? 

Let's rule some stuff out

    Other explanations have been offered in the past in order to try to make sense of the failures we see.  Heat, over-torquing, and gasket materials.  We'll take them one at a time, but not in that order.

1.  Gasket Materials.  Both gasket 'generations' are made of the same carrier material.  Nylon66.  Since that is the mechanical failure we see in the pictures above, that's the one we care about.  It's the same for both gasket sets.

2.  Over-torquing would show failures around the holes for the LIM bolts in the gaskets. We don't see that, and we know the compressive strength of Nylon is quite high. The failed areas are nowhere near these potentially over-torqued holes.

3.  Heat.  This can't be a factor based on the known properties of Nylon66.  Regardless of those properties, if temperature were the issue, the gasket carrier would fail in the 'dead' areas of the gasket, and not in the areas we see the failure.  The average maximum coolant temperature in the coolant ports is from 200-220 degrees Fahrenheit.  The intake ports see COOLER temperatures due to the intake air charge flowing through them.  In addition, the NON-DEX gasket shown here is from a supercharged engine that produces higher intake air temperatures due to compression before it gets to the gasket.


    So now let's talk about gasket re-designs.  GM 3100 and 3400 engines also ran DEX.  Those gaskets are known to have gone through design changes at the same time as the first redesign of the 3800 gaskets.  The material around the coolant ports (flexible something or other) wrapped around the nylon so that the coolant would not be in contact with the Nylon carrier.  The 3100 and 3400 engines never saw the latest revision, which replaced the Nylon carrier with aluminum.  Why?  My theory is that GM knew the dates that those engines would cease production, and that the 3800 would continue through 2008 or 2009.  In addition, the 3100 and 3400 engines are used in the smaller less-costly cars, while the 3800 is typically used in the 'flagship' models for each GM division.  That's called good business sense.



    My personal theories based on what I've shared with you in this report, is that ACIDIC EROSION breaks down the Nylon carrier material, and wicks around the silicone rubber seal until it starts breaking down the carrier around the intake ports.  This is based on the known properties of Nylon66 and the typical failures I've personally seen in 5 years as an Administrator on an automotive internet forum.  The fact that the 'dead' coolant port doesn't erode as badly is testament to the fact that the acid needs 'flow' or must be refreshed in order to start eroding the nylon.  It may also be true that the sludge that typically builds up in the dead coolant port protects the nylon carrier from further erosion.

    GM had choice between several corrosion inhibiting acids in their formulation of DEX, and probably didn't choose wisely.  Aftermarket OAT type antifreeze products use other types of OAT inhibitors that are not known for softening plastics.  This may have been pure dumb luck based on the fact that GM had covered themselves with a patent and a proprietary formula, or it may be that the new competitors in the market knew the dangers and chose more wisely.

    My personal suggestion is that anyone that currently has DEX in their car should change the LIM gaskets to the most recent design for their vehicle, and switch to Prestone Long-Life "mixes with any" (not DEX-compatible) antifreeze, which uses a different corrosion inhibitor that is NOT known to soften plastics.  There are rumors and theories around the internet that mixing the old glycol-based green coolant and DEX produces undesirable results like sludge, crystallization around gasket materials, and other scary things.  I don't suggest replacing the coolant in a DEX car with the 'green' old-school glycol based coolant for these reasons.  In fact, Havoline manufactures the 'new' DEX formula for GM, and they clearly warn consumers not to mix more than 10% conventional coolant (green) with DEX:

"Chevron recommends that this product not be diluted by more than 10% with conventional coolants."


    If DEX isn't a problem, why did GM re-design all these gaskets (twice for some of them) AND re-formulate DEX?  Is it coincidence?

    You can form your own conclusions from this page, but I would also encourage you to investigate it for yourself.  Perhaps someday we'll all know the answers without any doubt.




The information and opinions are my personal thoughts.

I am in no way affiliated with GM, DEX-Cool, or any other commercial venture.

Thanks to Don Blackwell and John Wikoff for their contributions to this page

Contributions were made by the members of