A Word of Caution About Organic Acid Type Coolants

[cbrTodd]

The subject of this post is my 1990 M923A2 with the Cummins 6CTA 8.3 engine. It was a 2009 "rebuild" at Kansas, including a tag on the front of the engine that says it has standard bore liners and standard size main / rod journals. When I bought the truck from GL in the fall of 2013, it had the standard green coolant in it, and it had a leaky / cracked radiator cap that it took me a while to find, so it got topped off a few times with 50/50 mix of Prestone green coolant. It always tested at -40F, so I left it in there. I was still doing the RV conversion so it did not get driven on the road for almost 2 years.

Fast forward to September of 2015 when I decided to install a block heater and found out how dirty that the cooling system really was. It had seriously brown coolant at the bottom of the radiator, and stayed brown for the first couple of flushes due to sediment in the radiator end tanks. I kept flushing it until I got clean water out the bottom, performing multiple heat up / cool down cycles to make sure coolant got moving through the radiator to clean it out. Not wanting to deal with coolant additives, and taking the advice of the guy at Napa, I selected the Zerex G05 heavy duty coolant, which is supposed to be a hybrid organic acid type (OAT) coolant that requires no additives. It has a Cummins spec listed on it saying it is approved, so I thought it was a good choice. While I had the system open, I added a coolant filter in parallel to the heater core as well.

In the fall of 2016, I started to notice coolant coming down the driver's side of the engine. I thought it was probably a result of one of the hose clamps being loose, so I went around and tightened every one of them, and most were somewhat loose. I confirmed when I started driving the truck this year that the coolant hadn't stopped coming down the side of the block though. After running out of other things to check, since the origin of the leak appeared to be from the head gasket joint, I decided to bite the bullet and put in a new head gasket. That's consumed every free minute I've had for the last week, but the truck is running again now, hopefully leak free. We'll see. When I drained the coolant this time, it was all the original color, but the coolant filter had probably a teaspoon of rusty brown grit in it when I cut it open. I flushed the engine once with hose water and once with distilled water before refilling it with the green stuff.

What I can confirm for you is that the head gasket used in my engine was the older Fel-Pro "Printo-seal" technology of a silicone sealing bead printed onto a metal carrier. OAT style coolants are known to attack silicone seals when they are not properly silicated. I found several spots near where I saw the coolant leak that this sealing bead had delaminated from the carrier and could have been the source of my leak. You can get a replacement of that same style of gasket from any number of places online, but I opted to go with the Cummins replacement part, which is a Dana "Victocor" style of gasket, with metal fire rings, Viton seals for oil passages, and a graphite carrier that seals the cooling passages. Yes it cost more, but it's a superior technology in my opinion. I know there isn't any silicone in the head gasket to fail in the future, but I still went back with green coolant and an SCA additive package, just in case there is another place in the engine that the OAT type coolant can cause pain for me.

I know this is a long post, but I wanted to put this information out there in the hopes of keeping anyone else from having to do this same job. I can't prove 100% that the OAT coolant caused my problems, but I have strong suspicions. It wasn't a hard repair per se, but it did take a lot of time and energy and required some creativity since I was doing it in my driveway without access to a crane or sufficient engine hoist.

From 2015 coolant flush:

From 2017 head gasket replacement:
Others have discussed this on steelsoldiers in the past (but on different vehicles), so I am attaching some additional reading below. Your experiences and opinions may vary.
https://www.steelsoldiers.com/showthread.php?70843-Zerex-ELC-Coolant
https://www.steelsoldiers.com/showt...rite-type-or-just-green-heavy-duty-type/page2

 

[simp5782]

Probably should talk to the NHC250 engine killer that swears the elc that is cummins spec is not killing his engine.


He will tell you to get the green coolant out.
Sent from my SM-G935P using Tapatalk

 

[cbrTodd]

I've read the NHC250 thread, and I believe that situation is quite different from mine. I have had zero performance issues with this engine, and all of the internal engine components that I investigated reflected the same. I do have a pyrometer installed, and I take action when it gets above 1200 F pre-turbo. The inside of the liners looked great, and the old head gasket showed no indication of combustion leakage, only the external coolant leaks. The head had no cracks and the injectors showed only light amounts of buildup, and all pop tested within 200 psi of the target according to the shop I had clean and test them for me. I'll never know the actual miles on the long block for sure, but I'd be surprised if it's very high.

Having been a GM owner since before I got my driver's license a couple decades ago, I've had plenty of experience with OAT coolant in the form of Dex-cool. None of that experience has been positive. It turns to an acidic goop if there's even the tiniest of leaks in the system, which most any engine has. It has a tendency to clog heater cores and radiators with all of the crud that it has eaten away from the less stable components in the system and dropped out of suspension in the hoses, etc. I've removed the Dex-cool from every vehicle I own, save for the one that is still under a factory warranty, and that one will have it removed as soon as the warranty is up.

I don't know why I thought that this experience would be any different. The 6CTA was designed at a time when the green stuff was the primary option, and this particular engine ran fine for nearly 3 decades with it until shorty after it got the OAT coolant added. It may have to be changed more frequently, but that's a small cost compared to replacing head gaskets or other more expensive components that weren't designed for this coolant. It's a mistake I won't be making again. Green coolant only for me from now on. "If the coolant ain't green, it doesn't belong in my machine!"