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The first time I mentioned it to my dealer they said they heard it but there is no solution from GM (Feb 2017). I switched dealers for service and mentioned it again at my final warranty work and they said they could not duplicate it but if it happens again or becomes super noticeable, they will repair it because I brought it up during warranty time frame. And by repair it I mean replace it with the new "surge bottle" that GM released about a year ago or so.

I then just researched the forum and found that topping it off with some dex cool 5050 slightly above the cut off line eliminates the water sound or minimizes it by 95%.
If you start the engine and quickly look at the surge tank you will notice a significant drop in coolant level. I believe this is what is causing the gurgling sound, if air is getting sucked into the heater core. Mine just started doing it about 3 weeks ago. My coolant level was about a half inch low.

Dexcool doesn't play nicely with air in the system. Things have improved since the introduction of Dexcool, but it does make you wonder about failed heater cores.

 

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Update.... So, my coolant level in the overflow was 3/4” below the seam. I took it to the dealership (only 5 miles) to get it topped off....and my level was ‘at the seam’ (while hot).
Dealer never topped it off. So - I got home - truck still at operating temp - I cracked open the overflow cap and allowed it to ‘burp’ for about 10 minutes. I never saw any air come out.

Fast forward to today.... I hadn’t heard the gurgle until driving home today. So, instead of going home, I drove around looking for a dirt mound to drive the truck up onto - to get the nose at an incline. Opened up the hood....cracked open the cap just enough... and there was an obvious & sizeable release of pressure from the tank. Put the cap back on and drove home. Crossing fingers.....

So - where should the fluid level be when the truck is COLD? I thought it was at the seam - but I honestly don‘t remember taking notice to that in all these years.
Where does the level end up when the truck is at operating temp? Since I obviously released a bunch of air, I’m assuming the level will fall even lower than it was before?
 

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Update.... So, my coolant level in the overflow was 3/4” below the seam. I took it to the dealership (only 5 miles) to get it topped off....and my level was ‘at the seam’ (while hot).
Dealer never topped it off. So - I got home - truck still at operating temp - I cracked open the overflow cap and allowed it to ‘burp’ for about 10 minutes. I never saw any air come out.

Fast forward to today.... I hadn’t heard the gurgle until driving home today. So, instead of going home, I drove around looking for a dirt mound to drive the truck up onto - to get the nose at an incline. Opened up the hood....cracked open the cap just enough... and there was an obvious & sizeable release of pressure from the tank. Put the cap back on and drove home. Crossing fingers.....

So - where should the fluid level be when the truck is COLD? I thought it was at the seam - but I honestly don‘t remember taking notice to that in all these years.
Where does the level end up when the truck is at operating temp? Since I obviously released a bunch of air, I’m assuming the level will fall even lower than it was before?
If you want the noise to go away for good then the cold level needs to be above the seam by 1/4” or so. The problem isn’t air trapped in the system that needs to be burped, it’s the low level in the surge tank causing air to be sucked in when cold. Nose up on a hill isn’t going to fix a low-coolant-induced problem.

Here’s where my level is when cold, I haven’t had the sound come back in like 2 years.




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That video is not correct. The Dexcool was not the cause of the gasket failure. The gasket was a poor design. The 3100,3400 engines came out in 1994 and they used the plastic gasket all the way until they replaced the gasket with an improved one in 2003. GM did not use Dexcool until 1996. I have replaced probably 100 of those gaskets. I have replaced the 1994-95 gaskets that did not have Dexcool used and the gaskets failed the same way. Dexcool got a bad rap. Maintain the vehicle and it works great. The old green coolant can have the same problems if you don't maintain it.
 

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If you want the noise to go away for good then the cold level needs to be above the seam by 1/4” or so. The problem isn’t air trapped in the system that needs to be burped, it’s the low level in the surge tank causing air to be sucked in when cold. Nose up on a hill isn’t going to fix a low-coolant-induced problem.

Here’s where my level is when cold, I haven’t had the sound come back in like 2 years.




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Thanks! So where does your level get to when its hot (operating temp)? I was surprised how high mine got when warm. I definitely need to add some. Tried to have the dealer top it off but it was already at the seam (warm). I’m gonna get some coolant today. This is mine now (cold).
 

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Thanks! So where does your level get to when its hot (operating temp)? I was surprised how high mine got when warm. I definitely need to add some. Tried to have the dealer top it off but it was already at the seam (warm). I’m gonna get some coolant today. This is mine now (cold).
My level when hot barely moves compared to the cold level, maybe 1/8”? Since I have the diesel my coolant temp is a bit lower then the gas engine (172F vs 210F? Not exactly sure how hot the gas engine runs but my coolant temp is a steady 172F except when towing up hill in the summer) so I have less heat expansion.


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It has been way too long since I did any thermodynamics calculations, but I would expect to see very minimal fluctuation in the level of water/antifreeze with temperature changes. A quick check shows the coefficient of expansion for water is 0.00012 per 1 deg F. So, if I am remembering this correctly, a 200 degree F increase in temperature would equate to a 0.024 increase in volume. My owners manual states the capacity of cooling system is 13.1 quarts or 419.2 ounces. So, I guess that is a 10 ounce increase, a little over a cup. More than I expected, but in the reservoir, that is maybe a 1/4" to 1/2" increase in height? Perhaps someone can add 10 ounces of fluid to their tank and let us know.

Pressure changes on a liquid will have minimal effect.

I haven't found a neat, clean coefficient for air, partially because it is not constant across a temperature range. I am going to suggest that I would expect it to be at least 10 times that of water. So, a little air trapped in the heater core, for instance, might make the same sort of change to the tank level as the 13 quarts of water do for the same temperature difference.

Pressure changes on the trapped air are going to have a larger effect. Also, air could be trapped in the liquid in the form of small bubbles, or even dissolved in the water. Increased in pressure and temperature could have other effects that are beyond anything I studied in thermodynamics during the Stone Age.
 

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Chevy won't really do anything to help after the bumper-to-bumper period. On the bright side, every time I hear the water rushing sound, I envision it as Chevy's (corporate citizen) way of subtly reminding us that global warming and sea level rising are truly imminent concerns...every time we drive our vehicles.
 

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Topped off the fluid level this morning.... Haven’t heard the gurgle since I burped it the other day. On my way home, stopped at my dirt mound and burped it again. A slight amount of pressure came out this time.

I’m more concerned about any leaks, etc. I did find a small pile of wetness right underneath the resevoir. Small hoses have dried coolant around the clamp. That’s not a concern to me. Looked around everywhere else for any signs of moisture - everything looks clean & dry. Oil is good too. Will keep an eye (and ear) on things.
Thanks Gang!!
 
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