[brownactive]

I am at 5500 miles now. For some time now when the car has sat over night when you first start it you can here a few seconds of water swoosh right in from on the drivers side dash. I know it is the cooling system, perhaps heater core filling as water pump moves the water. I assume there is not reason to worry. I just ask because I don't hear it in others cars I own.

 

[ZR2LIFE]

My Colorado does the same thing and I've heard it once or twice in the Trailblazer although it's not as noticeable. It's just air pockets inside the cooling system, mainly the heater core.

Steve

 

[brownactive]

it is only been more noticeable since the temps outside have dropped.

 

[OneAngryOtter]

I've only really experienced this with GM products and I assume it's partially to do with the fact that most GM coolant systems operate at 20+ PSI (higher than most other common manufacturers).

The pressure alleviates overnight (or when the car is off for a long period). My shower theory has been that the relatively high PSI, combined with thermal expansion of the coolant, then the simultaneous (gradual) loss of pressure and thermal contraction of the coolant can allow air bubbles to form in the heater core/elsewhere if parked at certain angles.

I've tried bleeding past GM systems of air but it never helps. I've heard it in my TB on occasion (particularly this past month with the cold weather) , as well as my Cruze before, but never as prevailant as with the Pontiac grand am I had years and years ago. In short, wouldn't worry about it, just a little weird quirk with GM engines. As long as it's not a persistent noise then the air is finding it's way out and not being trapped in the loop.

 

[ZR2LIFE]

I've also heard it's because some GM vehicles have the heater core placed higher which does create air pockets after the coolant gets cold and the volume changes. My 18 ZR2 does it on almost every cold start.