GM coolant elbow O-ring melted in one month. Why?

[Jazzy]

One month ago, 878 miles ago, as part of replacing the Lower and Upper Intake Manifold gaskets on my 2000 Bonneville SLE, I replaced both coolant elbows with GM elbows, an aluminum elbow from the water pump to the tensioner and then on to the heater hose, and a plastic elbow from the pump to the intake manifold. Flushed out the DexCool orange coolant and replaced with green Prestone coolant. Then the aluminum GM elbow started leaking coolant badly, from the larger end that goes into the tensioner and on to the heater hose.

The GM O-ring, orange, had just melted to something like limp spaghetti in tensioner unit to heater hose. (I have photos but don't know how to post them here.) Replaced it and other GM elbow with NAPA aluminum elbows, $18, and this time covered all elbow ends with black RTV goo that came with LIM gasket set. Replaced coolant with green Prestone again and bled, no leaks as of two weeks now.

Any ideas out there on why did the GM O-ring disintegrate? Bad o-ring?; fake GM part?; NAPA silicon grease that I coated O-ring with the first time?; GM O-ring dissolved by new green Prestone coolant?

I'm perplexed here.

[Archon]

I think that I recall that Andrew (Harofreak00) had trouble with the o-rings on some of the elbows. He replaced them as a matter of course.

[Namrepus28]

I know the Dorman version of that elbow is known for failure for that exact reason.

The GM made version is supposed to hold up much better. Are you sure it as an OE GM Part that was installed? If it was, then something else caused the O-ring to fail. (or it was just defective material)

[harofreak00]

Yeah the Dorman o-rings are horrible, but their aluminum elbows are fine. I've been replacing the Dorman o-rings with GM o-rings on every elbow I install as a preventative measure. I've never had a failure since.

I'm going to guess that you got a GM part that someone had swapped o-rings with or something like that. Fake GM part. Was it new sealed in a package?

[Jazzy]

The elbow was GM, ACDelco 91051-20, from Amazon, in a bag marked as from GM, https://www.amazon.com/gp/product/B00S0 ... UTF8&psc=1

[harofreak00]

I have no answers then, other than GM's quality is failing?

[Jazzy]

It is puzzling. I was guessing at posibilities, like the green coolant eating the GM O-ring, or the Silicon grease eating it. I had read all the good advice here which is why I bought the GM elbow. I just now gave it a one star review on Amazon with photos and hope the seller will respond.

[nos4blood70]

Per Andrew's advice, I used the aluminum elbows with GM o-rings. Been fine now for over 10k miles.

Having the GM o-rings side by side with the Dorman ones really made the difference obvious. The GM rings are more supple and squishy.

Not sure what happened with yours, maybe it is just a Dorman part that was re-branded.

[Jazzy]

Do you have a link or part number for the GM O-rings that you used? Thanks.

[harofreak00]

smaller: 25537068 x3
larger: 24502846 x1

I have these in stock if you want me to just drop them in an envelope for you. PM me if interested.

[Jazzy]

Thanks for those O-ring part numbers. I will get with you for the parts if the current repair starts leaking.

I'm trying to learn how to repair the Bonneville right the first time, but it seems that there is always a (long) learning curve for me the first time I repair anything on it that I haven't done before. And since this is my first and only Bonneville, if for example it took me four hours to replace the radiator the first time I did it, I could replace it again the next week or month in an hour. But the odds are I won't ever do that particular fix again, or if I do have to do it again in a few years, I will have forgotten how to do it quickly. But I'm willing to keep trying and learning how to do it myself, and this forum is a huge help for a raw amateur mechanic like me. I really appreciate you guys taking your time to answer questions you have heard so many times before.

I think these 2000-2005 Bonnevilles are still among the best looking big 4-door cars on the road today. They have about the same side silhouette and overall size as new or newer big BMWs and Audis, which of course are very expensive to buy and from what I hear, very expensive and hard to repair.

[MattStrike]

My thought here - there's only one supplier for those aluminum elbows. They supply all three brands with the same part (Gates, AC Delco, and Dorman), so they will all have the same problem. You aren't getting the GM orings on the AC delco aluminum elbow, you're getting the same thing that comes on the Dorman one.

The only way to get the GM orings is to order them via the numbers Andrew posted.

[Jazzy]

Thanks, will do that if the elbow leaks again, this time through the black RTV I slathered on. I started researching O-ring technology and there is a lot there to learn. It seems like making an O-ring that is only exposed to a maximum of about 250 degrees fahrenheit of coolant temperature and not under that much pressure should be easy and cheap, and there is no reason for any part supplier to use unsuitable O-rings.

Anybody think the GM O-rings can't handle green coolant, or the Napa 7651346 SIL Glyde Silicone grease that I used to lubricate the O-ring?

[peter]

Thanks, will do that if the elbow leaks again, this time through the black RTV I slathered on. I started researching O-ring technology and there is a lot there to learn. It seems like making an O-ring that is only exposed to a maximum of about 250 degrees fahrenheit of coolant temperature and not under that much pressure should be easy and cheap, and there is no reason for any part supplier to use unsuitable O-rings.

Anybody think the GM O-rings can't handle green coolant, or the Napa 7651346 SIL Glyde Silicone grease that I used to lubricate the O-ring?

I wouldn't advise using RTV with any rubber seal or o-ring. It's asking for a leak in my experience.

When I've done these coolant elbows, all I've ever installed with was some Vaseline to make sure it slides in straight. that's it.

[dougtoth]

I also had a problem with the Dorman aluminum elbows.
The elbow was fine but all the orings turned to mush and starting leaking.
After talking to Andrew I used the Dorman elbows with the GM orings that he suggested.
The Dorman orings lasted about 6 months.
The GM orings are now on about 2 years and no leaks.
I coated the orings with Vaseline before installation.
I also would advise you not to use RTV on them.

[Jazzy]

Thanks for the advice on no RTV. But that's what I did then because I had to get the car back in service, and will see if the elbows leak again. If they do, I'll be sure to get the real GM O-rings then, and skip the RTV. But I have also heard Vaseline can dissolve an O-ring, depending on what material the O-ring is made from. I've also heard that GM dealer mechanics would use RTV with the elbow replacements to avoid come-backs.

The O-ring that failed, melted in one month, 900 miles, was supposed to be a GM O-ring on the GM aluminum elbow from ACDelco Professional that I bought from Amazon, https://www.amazon.com/gp/product/B00S0 ... UTF8&psc=1 , (you can see the photos of the melted/dissolved orange O-ring with my negative review there). It came in a bag with an ACDelco label. I am still hoping that someone from ACDelco Professional will contact me in response to my review there.

I changed both O-rings on the Fuel Injectors when I changed the LIM two months ago; and I've changed O-rings on the fuel injectors and on the air-conditioning system on my Town Car, and never had a problem before with an O-ring just melting away like this one did.

[MattStrike]

I think some of the confusion is that this isn't neccessarily a GM part just because it is branded as AC Delco.
The Napa stuff is 99% likely to be the exact same thing re-branded.


I got bored, so if anybody wanted to upgrade these to HNBR or Viton from EPDM (I suspect it's really Nitrile but ), Here are the trade sizes:

-115 (11/16 ID, 7/8 OD, 3/32 cross-section O) (GM 25537068 is 17.02mm ID and 2.54mm thickness)
-117 (13/16 ID, 1 OD, 3/32 cross-section O) (GM 24502846 is 20.32mm ID and 2.54mm thickness)

[Jazzy]

Thanks for that info. There are many worse habits for the bored than actually measuring things and learning about O-ring manufacturing.

It should not be so complicated for a simple O-ring for a coolant bypass elbow. I wish they had designed it using a rubber hose elbow with hose clamps onto metal nipples, but they must have their reasons for the O-ring design. Using genuine GM O-rings, no doubt, as I will if my latest NAPA elbows and O-rings and my added RTV leaks again.

Maybe the real GM O-rings are a non-standard size, and ACDelco Professional and NAPA and Dorman just buy standard sized O-rings that are off by just a little bit, which could explain a slow leak. But how to explain an O-ring melting/dissolving in one month, 900 miles? Are the aftermarket ones made of a different material than the GMs? I started looking into O-ring types, and think most O-ring materials can handle ethylene glycol (coolant). But I can't find out what these various O-rings are made of. At this point, it's just intellectual curiosity wasting my (and yours) time.

But on the other hand, I don't want another O-ring failure leaking coolant while I'm out on the highway, so I may just change over now to the GM O-rings and not have to worry about it. I'm getting quicker with the mechanics of it. Maybe a new tensioner while I'm at it? Could the opening size in the tensioners for the elbows enlarge over 20 years and 190,000 miles? Mine looked good, and I cleaned them good.

[ron350]

Jazzy if you coated those o-rigs with decent RTV they are not going to leak.

PS: If you want to make sure your o-rings never leak buy a set of GM o-rigs and stash them in a drawer. The fact that you are prepared to replace the existing o-rings will guarantee the old ones will never leak.

[Jazzy]

I like that. Like the gasoline/propane electric generator I bought two years ago after Hurricane Irma in Florida knocked out electric power for a week in half of Florida and ruined $1,000 of food in my freezer. I cranked up that generator to test it, then cleaned out the old gas and oil and stored it away in my shed. Never lost power since, and I probably never will, as long as I have my generator sitting in my shed. Like the old joke asking a guy why he carried an elephant gun around his neighborhood: "Seen any elephants around lately?"