Gurgling noise from heater core at startup

[redbison00]

I have a 2020, with ~33,000 miles. Last fall it started making a gurgling noise at startup, from the passenger side, which I would assume is from the heater core. Doesn't do it everytime, but the majority of the time. It has never been low on coolant. Dealership flushed the heater core, and it still does it. Anyone else experiencing this issue?

 

[Keller]

See this post...

Thread 'Water sloshing at start up' https://www.trailboss.org/threads/water-sloshing-at-start-up.1762/

 

[redbison00]

Thanks!

 

[Keller]

Same thing right?

 

[redbison00]

Yep. Noise at startup only. Dealership flushed, didn't fix it. I'll have to look closer at coolant level in tank, or do some startups/running on a hillside, and see if the air will purge that way. Now that I think about it, it started after a trip last fall, where we were on some pretty steep hills, so I wonder if that shifted some air from the tank to the heater core. Thank you for pointing me to that other thread!

 

[Keller]

Keep us posted on your findings!

 

[Sly]

See this post...

Thread 'Water sloshing at start up' https://www.trailboss.org/threads/water-sloshing-at-start-up.1762/

Thanks that was my post

 

[Sly]

Yep. Noise at startup only. Dealership flushed, didn't fix it. I'll have to look closer at coolant level in tank, or do some startups/running on a hillside, and see if the air will purge that way. Now that I think about it, it started after a trip last fall, where we were on some pretty steep hills, so I wonder if that shifted some air from the tank to the heater core. Thank you for pointing me to that other thread!

I had the same issue . For me it was as simple as adding more coolant and after I did that I had the heater for a bit to get everything circulating and noise went away.

 

[redbison00]

I added more coolant, didn't help. Then I added some more, maybe 1 inch above the full line, and then went and drove up a steep hill and stopped. I then cycled between heat and AC, and turned the truck on and off a couple times. So far, it has not made the noise, going on a few days.

Question: Is the coolant cap on the overflow tank sort of loose? Like when it is turned all the way to when it stops, does it feel like it is loose?

 

[mrcolieman]

The surge tank cap is pressurized and, in my opinion, shouldn't feel loose... Maybe have it pressure tested to see if it has failed.

Best way to check/add coolant is to start with a cold engine on level ground (never open a hot cap as it is under pressure and hotter than the boiling point. The coolant will immediately boil and turn to steam). Slowly open the surge tank cap and add coolant to the cold full line. Start the engine, heat on highest setting and let the engine warm up with the cap off, 195*F as per the manual. This allows any trapped air bubbles to escape. Top off the surge tank to the full line (still with the engine running) and then replace the surge tank cap (if you shut off the engine with the surge tank cap off, it may overflow). Shut off the engine and let it cool. Recheck the level when cold and it should be at the full cold line. If it is still low, repeat the process.

 

[redbison00]

It would appear that the truck needs slightly more than the full cold line, to keep the trapped air out of the heater core.

 

[Cfaile]

I just bought a 2020 Silverado and it is gurgling behind the dash at start up only. What would cause air to get into the heater core? Everything about the truck works perfect, just have this noise on cold start ups.

 

[Sly]

Make sure your fluid is topped off

 

[redbison00]

Make sure your fluid is topped off

Yep. It would appear with mine that it needs a little than what the level mark shows on the tank.

 

[Sly]

Yep. It would appear with mine that it needs a little than what the level mark shows on the tank.

Did this ever fix it's self?