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Coolant

Discussion in 'Engine & Drivetrain' started by bradyjames, Feb 6, 2020.

  1. Larryjb

    Larryjb Full Access Member

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    Regarding Dexcool itself, the serious issue with it was on GM 3.8L engines. A number of them had faulty radiator caps which allowed coolant to push into the coolant reservoir (good), but then sucked in air as the engine cooled. The reservoir remained full while the radiator got air into it. The oxygen in the air mixed with the coolant, oxidized both the ethylene glycol and buffers (needed to keep the coolant at a healthy high pH). The oxidized glycol and buffers became acids, and the acids ate away at aluminum parts inside the engine. On the 3.8L especially, the heat combined with acidity (often pH 3-4, which is quite acidic) ate away at the nylon intake manifold gaskets. Nylon is normally a great material for gaskets unless it is exposed to heat and acid. Coolant would run between the lower intake manifold and block, so when the lower intake gaskets failed, water would get sucked into the engine causing a catastrophic failure.

    While our trucks have nylon intake manifold gaskets, coolant does not run through them, except maybe to the throttle body. So, Dexcool never really caused many catastrophic failures on the 5.3 or 5.7L engines. If you are concerned, get some test strips to check for acidity each oil change.

    As for me, I've had to fix so many things (water pump, "T"s, thermostat gaskets), I've changed my coolant way too many times. Yeah, I could have reused it, but for the cost of coolant I decided to change it anyway.
     
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  2. jonnytahoe

    jonnytahoe Full Access Member

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    Dex-cool or dexcool was introduced for the 1995 model year by General Motors. My'95 Tahoe came with information that was in with the Owners manual that said a New Coolant called Dex-cool was being used in your new Tahoe and to make sure you only use this coolant in the future and nothing else.
     
  3. PNW VietVet

    PNW VietVet Supporting Member

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    Same in my new 96 Tahoe.
     
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  4. HiHoeSilver

    HiHoeSilver Away!

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    Pretty close. ;) Except DexCool doesn't have ethylene glycol in it. It's an organic acid based coolant. That's what makes it different from the green stuff. Edit: This is wrong and corrected by @Larryjb below.

    According to Bill McKnight it was on the 3.1, 3.4, 4.3, 5.0, and 5.7s.

    Here's a fun video that came up in my hunting when I found green coolant in the Denali, and was trying to decide what to do. I ended up replacing it with Dex. Keep the faith. Lol.

     
    Last edited: Feb 8, 2020
  5. bradyjames

    bradyjames TYF Newbie

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    By faith do you mean the true doctrine? Lol :popcorn:
     
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  6. Larryjb

    Larryjb Full Access Member

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    Dexcool does have ethylene glycol, specifically mono ethylene glycol. See the MSDS link for the ACDelco Dexcool: https://www.orsrents.com/wp-content/uploads/2013/10/ACDelco-DexCool-Antifreeze.pdf

    The organic acid is the buffer. All automotive coolants have some sort of chemical buffer to prevent the coolant from becoming acidic. Decades ago, we had green coolant which used a silica based buffer. In the quest for long life coolants, GM switched to organic acid based buffers. Ford tried it in one vehicle for one model year and found it ate their water pumps. Ford uses a hybrid organic buffer which is a blend of organic and borate based buffers.
     
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  7. Larryjb

    Larryjb Full Access Member

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    Bill is very right about the gasket failures, but the 3.8 was also affected. I saved an intake gasket from my old 97 Lesabre with the 3.8L. I figure I was just a few months away from a catastrophic failure. I'll post a picture next week of it.
     
  8. HiHoeSilver

    HiHoeSilver Away!

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    Wow. I can't believe that in all my craziness to decide which to run in the Denali, nothing I saw pointed this out. Or, frankly, that I have never checked the sds for myself. Thanks for this.
     
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  9. Larryjb

    Larryjb Full Access Member

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    I've come across this misconception before. Having a graduate degree in chemistry helps me to question these things. When I had my Buicks I learned a lot about the Dexcool.

    Nylon gaskets are perfectly fine when exposed to acids, fine when exposed to heat, but fail when exposed to both. In a perfect world where owners keep up with coolant changes and monitor the fluids, those gaskets would likely still be good 25 years later. My dad's 97 Tahoe is still good today with it's nylon gaskets.
     
    Last edited: Feb 8, 2020
  10. jonnytahoe

    jonnytahoe Full Access Member

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    .
     
    Last edited: Feb 8, 2020
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