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Old 12-01-2010, 04:01 PM
TomJ01 TomJ01 is offline
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Default Dexcool vs. other coolants

I am still hearing Duramax owners discussing the Dexcool issue. I know GM insists it must be used. Is there any definitive information as to the advantages/disadvantages of changing from Dexcool to another brand of coolant/antifreeze? I am aware of previous lawsuits etc., but by now there must be expert guidance on this question. THANKS!
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Old 12-01-2010, 07:46 PM
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15 years, no problems....
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Old 12-01-2010, 10:07 PM
rapidoxidationman rapidoxidationman is offline
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10 years no issues, but I've heard that mixing it with other types is very badn(sludge problems).

I also tend to not try to outthink the engineers...
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Old 12-02-2010, 08:17 AM
madmatt madmatt is offline
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I've been putting it in them since they came out and have never had an issue.
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Old 12-02-2010, 04:21 PM
Kennedy Kennedy is offline
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The Dex Cool lawsuits in my opinion stem from GM's (Chev in particular) inability to seal an intake gasket to save their own lives. Now that the newest engines don't have coolant in the intake this seems to have pretty much stopped. Nothing changed, just the abscence of air from leaky gaskets.

The 6.5 used Dex Cool for many years also and I have never seen a lick of corrosive evidence except again for where it would leak ie: heater feed nipple on water crossover. I did make the mistake of leaving coolant between the upper rad hose and stat housing and this pitted the housing pretty bad outward of the clamp.
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Old 12-03-2010, 12:01 PM
madmatt madmatt is offline
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ditto to what john said. for a while there GM might as well have not even used gaskets on lower intake manifolds,, they probably would have leaked less. Since that happened about the time dexcool was put in everything, it got the blame.
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Old 12-03-2010, 12:39 PM
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Arrow Texaco/Havoline Dex-Cool - reprint from 2003

Texaco/Havoline Dex-Cool
By - 2003

GM made the switch to the new orange-colored Texaco/Havoline Dex-Cool in the 1996 model year due to its longer service cycle, longer water pump seal life, high temperature aluminum protection, and a higher coefficient of heat transfer. At the time of introduction, this new coolant came with a recommended 100,000 mile maintenance cycle. Shortly thereafter, GM began recommending a 5 year/150,000 mile coolant maintenance cycle for the 6.5L (and Duramax 6600) turbo diesel engines because of the improved long-life characteristics offered by this new coolant. According to a 1998 NARSA (National Automotive Radiator Service Association) report, Texaco/Havoline began recommending the average cycle life of this new silicate-free orange coolant be increased to 250,000 miles and beyond in other applications.

DEXCOOL is a registered trademark of General Motors Corporation, used under license by Texaco Lubricants NA. Dex-Cool contains an ethylene glycol base along with carboxylate corrosion inhibitors (organic acid) for an advertised improvement in rust and corrosion protection. For more information about Dex-Cool, you can call 1-800-782-7852 or visit on the web.

Conventional coolant, such as Prestone brand antifreeze/coolant shown above (green dye) is also an ethylene glycol based coolant, but uses a blend of silicate corrosion inhibitors. Green-dyed silicated coolants represent the type of formulation used by GM prior to the introduction of Dex-Cool. For continued cooling system protection, Prestone recommends an annual flush and fill when using a silicated ethylene glycol coolant. This is necessary because the concentration of conventional rust and corrosion inhibitors (silicates) tend to decrease over time. Prestone also produces a silicate-free organic-acid based coolant, but we have no experience with this product. For more information about Prestone brand automotive coolants, you can visit them on the web at

GM does not recommend installing an organic-acid based coolant in systems with a copper/brass/soldered radiator because of a potential for lead corrosion. However, Prestone says their organic-acid ethylene glycol tests have shown no problem with lead corrosion, and recommends the use of their organic-acid ethylene glycol coolant in either copper/brass or aluminum systems. Our tests here at The Diesel Page with Texaco/Havoline Dex-Cool and copper/brass/soldered radiators have shown no internal cooling system deterioration after nearly 120,000 miles and four years of use (6.5TD).

Converting a system containing silicated coolant (yellow/green dye) to an organic-acid coolant (orange dye) requires a thorough system flush to remove all traces of the original silicated ethylene glycol coolant. These two coolants are somewhat compatible, in that you won't damage your engine or cooling system with a mix, but mixing coolants containing carboxylate and silicate corrosion inhibitors will shorten the service cycle to that of silicated ethylene glycol. Copyright 2003 by The Diesel Page

While Texaco/Havoline recommends a "good quality tap water" when preparing a 50% Dex-Cool solution, both NARSA and The Diesel Page recommend using distilled water to dilute Dex-Cool. Chlorinated or hard water can affect the long-life properties and corrosion protection offered by any automotive coolant.

However, mixing two unrelated formulations of organic-acid ethylene glycol coolants is a concern. There are several different chemistries used for long-life coolant that can appear as pink or orange or red. They may not be compatible with one another. Europe has their own formulation, Japan has theirs, Chrysler Corporation has theirs, and Texaco/Havoline has theirs. If someone topped off a 6.5 or Duramax cooling system with a non-compatible coolant, undesirable consequences could result. If in doubt, look for a description on the bottle indicating that it meets specification GM-6277M or ASTM D-3306. I always carry a gallon of pre-mixed Texaco/Havoline Dex-Cool (with 50% distilled water) with me whenever I travel, to help mitigate this possibility.

We have learned that an air/coolant interface within the engine or cooling system could create an environment for aluminum or iron corrosion when using Dex-Cool. Not coincidentally, GM incorporated an air-bleed screw in the 6.5L & Duramax 6600 thermostat housing. This provides a means to vent air from the cooling system. Additionally, the coolant surge tank is also designed to remove air from the cooling system. So, unless there is some sort of engine or cooling system failure (or inadequate initial fill), there should never be an air/coolant interface in your 6.5 or Duramax cooling system.

A recent class-action suit has been brought against GM for cooling system corrosion involving 4.3L engines used in GM's late model Blazer, Jimmy, Olds Bravada, Sonoma, and S10 pickups. As reported in the May 22, 2003 issue of The Columbus Dispatch, GM stated that it "is aware of concerns about Dex-Cool. However, those problems involve customers who ran their cooling systems for an "extended period of time" -- 15,000-20,000 miles - with low coolant levels." GM went on to say that "There are 35 million to 40 million GM vehicles on the road that use Dex-Cool, and the overwhelming majority have experienced no problems with the cooling system." As stated earlier, we have also identified a problem with a coolant/air interface, and the potential for corrosion as a result. We also know that cooling system performance (when properly filled with a 50% Dex-Cool/distilled water solution) will surpass those using a green silicated ethylene glycol coolant.

As a result of this class-action suit, some owners of the GM full-size diesel pickup engines have become concerned about the possibility of cooling system corrosion in their own vehicles. Ensuring the absence of air in your cooling system should preclude any sort of corrosion problem. If you notice the coolant surge tank level rising or falling beyond the hot/cold levels, you may need to investigate the cause. An external coolant leak, a faulty cooling system pressure cap, a leaking head gasket or some other sort of failure could cause an air/coolant interface to develop inside your engine. This is a bad thing.

Some have suggested draining the Dex-Cool and refilling with a green ethylene glycol coolant. Before taking that step, consider this: This radiator core image illustrates the result of improper cooling system maintenance after the vehicle accumulated just 135,000 miles. Perhaps more importantly, it also shows what the combination of improper maintenance and green silicated ethylene glycol can produce.

Human nature being what it is, too many people will neglect certain systems in their vehicle. The radiator shown here, the engine and the cooling system were replaced soon after that photo was taken in 1998, and the new cooling system and 6.5TD engine have subsequently accumulated 120,000 miles on a single initial fill of Texaco/Havoline Dex-Cool (& 50% distilled water). The internal condition of the radiator and thermostat housing still appear like new. If the Dex-Cool filled systems survive better when neglected, that's a good case all on its own to use Dex.

Some have blamed cylinder head gasket failures on Dex-Cool. However, here at The Diesel Page, we know that the primary problem with 6.5 head gaskets is directly related to the factory 21.5:1 compression ratio. During the 2001 Rendezvous in Ohio, Matt Koning, CEO of Peninsular Diesel told our group during a seminar that Peninsular had never replaced a failed head gasket on any of their 18:1 compression ratio marine 6.5L engines - not a single one in 10 years of 6.5 marine engine production. In contrast, head gasket replacement for the "on-road" 6.5TD engines (with their 21.5:1 compression ratio) is a somewhat routine occurrence between 80,000 and 200,000 miles.

There is no discernable difference in 6.5 head gasket reliability for engines built prior to or since the introduction of Texaco/Havoline Dex-Cool. If Dex-Cool created an endemic cooling system corrosion problem with the 6.5 and Duramax engines, The Diesel Page would be well versed in the science and chemistry behind it (by the shear volume of routine email messages and phone calls). Since The Diesel Page began in early 1996, a question about coolant type has not been an issue we've dealt with till this article.

Continued next post:

Copyright 2003 by

Last edited by More Power; 01-13-2011 at 02:13 PM.
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Old 12-03-2010, 12:41 PM
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More Power More Power is offline
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The Diesel Page recommends the continued use of Dex-Cool long-life coolant, for those vehicles so equipped from the factory. We also recommend all 6.5L and Duramax 6600 owners monitor the coolant surge tank level to help reduce the possibility of an air/coolant interface developing inside your engine or cooling system.

In closing: If there is an unbiased organization that would know about engine and cooling system corrosion problems involving GM vehicles and Dex-Cool, NARSA (National Automotive Radiator Service Association) would have the facts and would be able to make the most informed recommendations regarding engine coolant use. I contacted them in preparation for this article. What follows is an e-mail exchange I had with their Technical Services Director and Technical Services Manager. Copyright 2003 by

My first email message to NARSA:

Hello Narsa,

I'm the editor of

Our's is a GM diesel pickup enthusiast organization that covers the 6.2L/6.5L and Duramax 6600 diesel engines. In the late fall of 1998 I had a local NARSA shop rebuild a radiator for a special project we were involved with, and I picked up a copy of your newsletter (volume 12, No. 5 Sep/Oct 1998) that was entitled "Your Best Choices for Antifreeze/Coolant Top-Up and Service".

In this newsletter, Texaco/Havoline Dex-Cool was discussed along with other coolants available world-wide.

Recently, a class action suit has been initiated against GM for cooling system corrosion involving engines and cooling systems in their mid-size SUV's. As a result, some owners of the GM full-size diesel pickup engines have become concerned about the possibility of cooling system corrosion in their own vehicles.

I am not interested in any legal matter, but would like to know what NARSA's experience has been with Texaco/Havoline Dex-Cool, regarding cooling system corrosion. I hope to write an article covering this issue, and offer our members a correct and comprehensive discussion about Dex-Cool. If you can provide more background and technical information on this subject, I would very much appreciate it.

Thank you,
The Diesel Page

NARSA's Mark Dwyer's reply:


We're familiar with the class action lawsuit to which you refer -- it was inevitable after all of the issue's GM has had with cooling systems in their trucks equipped with the 4.3L engine. We've written extensively in our own magazine (the Automotive Cooling Journal) as well as in our two technical publications -- the NARSA Service Reports and Radiator Reporter -- about the problems with Dex-Cool inside these systems.

The 4.3L engines used in GM's late model Blazer, Jimmy, Sonoma, S10 pickup and Olds Bravada models are subject to severe cooling system contamination. The muddy, rust-colored substance is mostly iron oxide from the cast iron engine. In many instances the rusty material develops in quantities large enough to plug radiator and heater core tubes, and its abrasive characteristic can shred a water pump impeller. Vehicle owners may complain of engine overheating and poor heater output.

GM says the rust problem is triggered by a "low coolant" situation over an extended period of driving. When the cooling system is underfilled, trapped air triggers massive oxidation of the engine's cast iron surfaces. The factory-fill Dex-Cool isn't believed to be the cause, and in fact GM says mechanics should continue to use the Dex-Cool product for top-offs and flush-and-fills on these 4.3L engines.

To cure the rust problem, we advise adhering to GM's 60-step flushing procedure. Yes, sixty steps. The key part of the procedure is to use a super-strong acid-based flush product, with neutralizer. You can order the flushing chemicals from GM under part number 12346500. This is nasty stuff, so be careful to follow all instructions and precautions. It bears the Prestone name, but should not be confused with gentler Prestone flushing agents sold at parts and discount stores.

GM's flush procedure is tedious and may not always be successful. Water pumps may have to be replaced, along with severely plugged heaters and radiator cores. A new thermostat and radiator cap are mandatory.

Based on interviews with the major domestic carmakers and aftermarket coolant manufacturers, we recommend that our members follow these guidelines when servicing coolant:

Always use the type of coolant specified by the vehicle manufacturer. For long-life coolant, either use the OE brand or, if you use an aftermarket product, make sure the manufacturer states that the coolant meets OE specifications.

Never mix different long-life coolants.

Never add a long-life coolant to a conventional coolant or vice versa except in emergency situations when there is no other alternative. If the two coolants are inadvertently mixed, the vehicle's entire cooling system should be thoroughly drained and flushed as soon as possible and refilled with the proper type of coolant.

If a retrofit to an older system is approved by the carmaker or coolant manufacturer, a thorough drain and flush of the old coolant is essential. A long-life coolant in an older vehicle, especially with a copper/brass radiator, should be frequently tested for signs of corrosion. In most cases long-life coolant cannot be used to its full service life in an older vehicle.

Avoid using chlorinated water with organic-acid-based coolants like Dex-Cool.

I'm not the technical guy around here, but to date, we've not published anything (as far as I can tell) about similar problems on 6.2L/6.5L and Duramax diesel engines on vehicles with Dex-Cool as the factory fill. However, I've asked Joe Ettwein, our Technical Services Manager to also respond to your inquiry.

Good luck!

Mike Dwyer, CAE
Executive Director - National Automotive Radiator Service Association (NARSA)
On the Web:


NARSA's Joe Ettwein's reply:

NARSA really avoids taking a position regarding products, however there's no denying that our members are all too familiar with vehicles plagued with "DexCool-related" cooling system failures. I put the quotation marks in because they are not my or NARSA's words or convictions.

The real problem with DexCool in a GM vehicle is the presence of water and air - especially the air. Most of the time I find that the pressure cap won't seal at the radiator filler neck. When this happens, the system(antifreeze and water) is exposed to air. Everyone knows that water, air and metals will get together to form some sort of rust/corrosion without fail. GM vehicles have an added, which appears to accelerate the development of internal rust and sludge within the cooling systems.

If a cooling system fills with rusty sludge, it must be flushed and flushed and flushed some more...til there's no trace of rust and/or sludge. Repair the radiator filler neck as described below and refill the system with a 50/50 mixture of distilled water and antifreeze.

I hope this has helped you to understand what takes inside a GM cooling system containing DexCool, water and air. One simple fix for the poor sealing qualities of the pressure cap is to wrap sandpaper around a 2x4 and basically plane off the imperfections on the top surface of the neck opening to allow the cap to seal properly. Don't forget to stuff a rag or paper towel into the neck before beginning the sanding process. Use a pressure tester to check the cap and the filler neck for correct sealing.

If you have further questions, let me or give me a call.

Best regards,

Joe Ettwein
NARSA Technical Services Manager

Continued next post:
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Old 12-03-2010, 12:42 PM
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More Power More Power is offline
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My second email to NARSA:

Hi Joe,

Thank you for your reply.

I was aware of the coolant/air interface problem. The GM 6.5 and Duramax cooling systems are monitored with a "Low Coolant" indicator. Engine or cooling system problems that result in a lowering of the coolant level usually result in a warning to the driver. Our personal vehicles equipped with the GM 6.5L or Duramax diesel engines and Dex-Cool have not experienced any cooling system issues.

Do the 4.3L engines used in GM's late model Blazer, Jimmy, Sonoma, S10 pickup and Olds Bravada models not have a low coolant indicator? These engines and models are included in a class-action lawsuit, resulting from cooling system and engine corrosion due to Dex-Cool.

Thanks again,

Second reply from: Joe Ettwein
NARSA Technical Services Manager

Yes the 4.3 GM engines have low coolant warning systems, including my 2002 1500 Silverado w/ 4.3 V6. The interesting thing is that if the radiator pressure cap does not seal at the filler neck, the coolant escapes at that location and since the siphon is non-existent, the radiator coolant level can deplete even though the reservior is at the proper level...simply looking at the level in the jug is not enough.


Second reply from: Mike Dwyer, CAE
Executive Director - National Automotive Radiator Service Association (NARSA)


If there aren't any problems, I wouldn't replace the Dex-Cool with conventional green if for no other reason than it will void the manufacturer's warranty. If the vehicle is out of warranty, of course, it wouldn't matter. If you switch, you'll also lose the 5-year, 150,000 mile long-life coolant service.


Copyright 2003 by
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Old 06-21-2011, 02:34 AM
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Canadian Cowboy Canadian Cowboy is offline
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There is nothing wrong with Dexcool coolant,the issue first arose with head gasket leaks,the molecules are smaller and will leak whereas the traditional green coolant will not.
Manufactures had to redesign head gaskets and head/engine block finishes to prevent leakage.
They have finally corrected it for the most part.
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