Coolant

[Larryjb]

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.

 

[JonnyTahoe]

I drive a 2005 Tahoe z71. I Have about 160k miles on it.

What coolant should I be using in it? I know it calls for dex-cool but I’ve read on other GM and Chevy forums that it’s bad and eats away seals and gaskets over time.

So when I bought it I put in a new radiator and water pump and filled it up with Peak 50/50. I haven’t had any issues with it. It’s been running great for the past year and it looks just as clean as the day I put it in.

Recently, I had a small leak. Turns out my thermostat housing wasn’t tightened down to spec. That was my own fault. My mechanic noticed that I was using the wrong coolant though and mentioned that I should be using dex-cool - so here I am lol. He claims that GM has a new dex cool formulation that doesn’t eat away at seals and gaskets and recommended that I switch.

Is there truth to this? Should I stop using Peak 50/50 and switch to the new dex cool?

Any insight or wisdom would be much appreciated.

Thanks

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.

 

[OR VietVet]

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.

Same in my new 96 Tahoe.

 

[HiHoeSilver]

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.

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.

 

[bradyjames]

By faith do you mean the true doctrine? Lol

 

[Larryjb]

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.

 

[Larryjb]

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.

 

[HiHoeSilver]

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.

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.

 

[Larryjb]

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.

 

[JonnyTahoe]

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