The Dexcool wars

[Dr. John T. Welch]

Soon we will celebrate the 26th anniversary of Dexcool, the GM extended service factory fill engine coolant formula used for for most of its  automotive/truck applications. It has been blamed and scapegoated for years as the cause or contributor for many engine and cooling system maladies in our vehicles. It employs organic acid based coolant chemistry  that differs from the traditional ethylene glycol/silica formulas of the past. Everyone seems to have their own Dexcool horror story to recount.

This is a photo of a representative sample of Dexcool I recently drained from my '96 GMC Yukon after 6 years and 50,000 miles of punishing urban service that includes the brutal desert summer heat of Phoenix. Owing to meticulous cooling system  maintenance with focused attention to hose and  component connection integrity as well as radiator cap seal, there has been virtually no exposure to atmospheric air which is the death sentence for Dexcool and most everything in contact with it: the recipe for orange oatmeal. The radiator, heater core and engine cooling passages are pristine on the
350 Vortec V-8 at 135,000mi.

Yes, there are a lot of Dexcool related engine problems.  In my experience most of them feature Dexcool as the  innocent bystander or abused wife.  Most of the difficulty has been addressed long ago  and found to be design flaws in gaskets and seals, poor vehicle maintenance, and catastrophic mechanical failure of non cooling system origin.
   
 
 

[James Landi]

Dr. Welch,

I trust you're not going to drink that fluid... yet,your presentation does make it look like a fine, aged scotch whisky!  As for your sagacious comment about scapegoating, that appears to be a national pasttime. Rather than drilling down on careful analysis, science, and empirical facts, it "feels" so much better to heap blame by ignorantly confusing cause and effect, denying scientific research, and simply ignoring all of the authoritative information that's now so conveniently and readily  available on the internet. Having said more than enough, I suggest that we must press on!  Happy day, James   

[fishnjim]

You're attention to maintenance is what you owe the success to.  Preventative maintenance is good/best practice.
Regular old fluorescent yellow green prestone will hold for 6 years, too.  But best to change it on schedule and not press your luck.  I like 5 years, easy to remember but that was based on the old pricing, so may have to re-think.   
Part of the formulation issue was the mixed use of components with aluminum and perceived toxicity of EG based.
There's some build up of solubles/corrosion products, that should be purged.  The inhibitors dissipate over time. 
The color is only dye and that too will change/degrade/shift to indicate pH issues..  There's test kits too.
Always use distilled water, if you dilute your own. 

[Eric DeVirgilis CLC# 8621]

Over a wide variety of GM vehicles, my experience has been that Dexcool didn't do well in mid to late '90s Blazers/S10 trucks with the 4.3 Vortek where the stuff turned into a mess. With almost everything else, the same coolant remained clean in vehicles with well over 100,000 miles with never having been changed. I've heard different stories over the years but I've never gotten a clear answer why Dexcool worked well in some vehicles while in others it did not. 

[Dr. John T. Welch]

Dr. Welch,

I trust you're not going to drink that fluid... yet,your presentation does make it look like a fine, aged scotch whisky!  As for your sagacious comment about scapegoating, that appears to be a national pasttime. Rather than drilling down on careful analysis, science, and empirical facts, it "feels" so much better to heap blame by ignorantly confusing cause and effect, denying scientific research, and simply ignoring all of the authoritative information that's now so conveniently and readily  available on the internet. Having said more than enough, I suggest that we must press on!  Happy day, James

Thanks for your insight.  It appears that my photo had its desired effect: to show some excellent, unrestored and original Dexcool in a flattering way.   

[Dr. John T. Welch]

Over a wide variety of GM vehicles, my experience has been that Dexcool didn't do well in mid to late '90s Blazers/S10 trucks with the 4.3 Vortek where the stuff turned into a mess. With almost everything else, the same coolant remained clean in vehicles with well over 100,000 miles with never having been changed. I've heard different stories over the years but I've never gotten a clear answer why Dexcool worked well in some vehicles while in others it did not.

I've never gotten clear answers on that subject either.  In casual discussions with some GM engineering types, several now retired, the following is offered:

1) For MY 1996 a comprehensive across the board effort was undertaken to make all GM engine and power train  emissions critical systems more robust to enable reliable OBDII  performance during the federally mandated emissions compliance period.  The actual field result with Dexcool use  was somewhat uneven due to intrinsic differences among various engine designs then in production. Intake manifold gasket sealing was especially vulnerable for some engine families,  and a source of much Dexcool dismay. Major improvements for intake manifold gaskets and seals were necessary and implemented by GM , but a lot of engines failed both in and out of warranty before they could be applied. MY 1996 is the "continental divide year" for North American venicle  emissions regulation and control strategies, and extended life  Dexcool formulas in cooling systems are big  part of 1996 OBDII and beyond industry wide. 

2) The basic chemistry involved with Dexcool is sound and proven in use as the contemporary ICE coolant formula of choice. 

[hornetball]

Interesting.  My "guess" was that switching to Dexcool was related to using aluminum for blocks and heads.  In fact, it was for emissions.  Learn something new everyday.

[Dr. John T. Welch]

My understanding is that it was part of a comprehensive improvement of engine wear and maintenance "pain points" to reduce interval  maintenance service but  still comply with mandated emissions standards and retain  warranty backed product performance. Look at some of the period product promotional brochures.   Included in these modifications but not so obvious were: reductions in viscosity specs for engine lubricants, incorporation of serpentine belt accessory drive systems, longer interval lubricant changes, modifications to transmission/transaxle, transfer case and drive axle lubricant specs, constant tension spring type hose clamps, changes in polymers used in cooling system hoses to prolong life and improve seal and numerous other internal invisible upgrades to seals, fasteners, connections, etc. There is a big difference between pre and post 1996 vehicles although they appear deceptively similar.   

[fishnjim]

SAE J1034, SAE J1941, SAE J814
It's all in there if you look at the historical progressions. 
Much ado about nothing as they say.  It's still EG based "antifreeze" in the final analysis.   
Chemistry doesn't change, but new reactions are discovered every day...
Protecting the machinery is only one aspect.  Heat transfer considerations, too.
Organic alcohols will oxidize to organic acids with heat and air in the presence of water.  Glycol is a diol - 2 alcohol/molecule so readily susceptible to oxidize.(But needs them to be soluble)  Acids react with metals/metal oxides to various degrees.  Acid can catalyze the reaction, so once it goes, it can go quickly.
Move to aluminum did require some inhibitor shifts.   Aluminum protects itself with oxide, but if you remove that oxide layer, it's readily susceptible to corrode.  In thin section, like a radiator, it don't take long for weeping.  Aluminum for light weighting was a mileage thing, from the CAFE stds. push.  There were periodic pressures on copper pricing, too.  In brass, it's the solder that takes the hit mostly and needs protected.  Competing interests.
Anytime you change something and other things at the same time, expect some unexpected "bumps".  It has to do with the statistical combinations of probabilities.  It's why the old adage about "only change one thing at a time" isn't always practical.  Risk in inherent in everything.
Context: It was billed as lifetime or permanent, but that got into legal issues.  There was a lack of recycle of spent coolant "du jour", so was aimed to decrease waste as well.  These were instigations of Clinton/Browner EPA times.  How well I know them.  I bear scars...
Create a problem then go solve it, but better to have the solution ready and look like a genius!

[Bryan J Moran]

Pardon my ignorance but when introduced and applied over the years, is Dexcool supposed to be mixed with distilled water or was it a standalone "coolant" product?

[TJ Hopland]

I have always seen it both ways just like classic green which you can buy premixed 50/50 or full strength.

I haven't had any issues with the stuff.   I wonder if one reason some cars had issues was that the layouts tended to have lots of places to trap air?   Radiator was no longer the high point in the system so they don't bleed naturally? 

[Dr. John T. Welch]

The product instructions give a dilution formula for full strength Dexcool according to the desired protection against freezing. 

The main vulnerability of Dexcool is exposure to air and atmospheric oxygen.  This usually occurs with faulty connections, deteriorated hoses, and damaged cooling system components. The early leaks are insidious and usually allow only vapor escape at first so there is no visible liquid, but the system pressure is reduced with a loss of cooling capacity.

Many engine layouts require bleeding of air after filling and have specific ports for doing so. Failure to accomplish this leaves damaging air in the system which will not self-bleed.