Bubbling under the dash, no heat

More then likely the heater core is partially plugged or leaking. Here are some guides that help with this specific issue:

https://www.2carpros.com/articles/vehicle-bubbling-noise

Even though the temperature is consistent with a functioning heater core, it still does not eliminate it as a possible cause. Did they provide the temperature differences between the hoses? The outlet should be about 20 degrees cooler and when the heat is on max the hoses should be too hot to hold.

https://www.2carpros.com/articles/car-heater-not-working

Let us know this info and we can go from there, but I am thinking the heater core needs replaced. so here is the process just in case. Thanks

Hi,

I'm not sure what all was checked by the dealer, but there is a technical service bulletin related to no heat on this vehicle. It is caused by air in the system. Here are the directions for properly bleeding the system. See if this is what they did.

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2012 Chevrolet Volt L4-1.4L Elect
Cooling System Draining and Filling
Vehicle Engine, Cooling and Exhaust Cooling System Service and Repair Procedures Cooling System Draining and Filling
COOLING SYSTEM DRAINING AND FILLING
Cooling System Draining and Filling

Special Tools
* GE-26568 - Coolant and Battery Tester
* GE-47716 - Vac-N-Fill Coolant Refill Tool
* GE-42401-A - Radiator Cap and Surge Tank Test Adapter

For equivalent regional tools, Refer to Special Tools See: Cooling System > Electrical / Mechanical Repair > Special Tools

Draining Procedure

Warning

To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot.

1. To drain the engine radiator, remove the engine coolant temperature sensor fron the radiator. Refer to Engine Coolant Temperature Sensor Replacement See: Engine - Coolant Temperature Sensor/Switch > Removal and Replacement > Engine Coolant Temperature Sensor Replacement

pic 1

2. Attach the venturi assembly to the vacuum tank.

Pic 2

3. Attach a shop air hose to the venturi assembly.
Ensure the valve on the venturi assembly is closed.
4. Attach the vacuum hose to the vacuum tank.

Pic 3

5. Attach the extraction hose to the vacuum hose.
6. Insert the extraction hose into the radiator outlet front hose until the extraction hose contacts the bottom of the radiator outlet hose.

Pic 4

7. Open the valve on the venturi assembly to start a vacuum draw.
8. Use the extraction hose to draw out coolant until the radiator is empty.
9. The vacuum tank has a drain valve on the bottom of the tank. Open the valve to drain coolant from the vacuum tank into a suitable container for disposal.
10. If a complete engine block drain is required, remove the engine block drain plug.
11. To drain the heater cooling loop, remove the hose from the inlet of the heater water auxiliary pump. Refer to Heater Water Auxiliary Pump Replacement See: Auxiliary Water Pump > Removal and Replacement > Heater Water Auxiliary Pump Replacement
12. Inspect the coolant.
13. Follow the appropriate procedure based on the condition of the coolant.

Normal in appearance--Follow the filling procedure.
Discolored--Follow the flush procedure. Refer to Flushing See: Cooling System > Procedures > Flushing

Vac-N-Fill Procedure

Warning

To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot.

Note: To prevent boiling of the coolant/water mixture in the vehicles cooling system, do not apply vacuum to a cooling system above 49°C (120°F). The tool will not operate properly when the coolant is boiling.

Pic 5

1. Install GE-42401-2 - Radiator Cap and Surge Tank Test Adapter into the surge tank fill neck.
2. Install GE-42401-3 - Radiator Cap and Surge Tank Test Adapter to the surge tank fill neck.
3. Attach the Vac N Fill cap to the GE-42401-3 - Radiator Cap and Surge Tank Test Adapter.

Pic 6

4. Attach the vacuum gauge assembly to the Vac N Fill cap.

Pic 7

5. Attach the fill hose to the barb fitting on the vacuum gauge assembly.
Ensure that the valve is closed.

Pic 8

Note: Use a 50/50 mixture of DEX-COOL antifreeze and de-ionized water.

Always use more coolant than necessary. This will eliminate air from being drawn into the cooling system.

6. Pour the coolant mixture into the graduated reservoir.
7. Place the fill hose in the graduated reservoir.

Note: Prior to installing the vacuum tank onto the graduated reservoir, ensure that the drain valve located on the bottom of the tank is closed.

8. Install the vacuum tank on the graduated reservoir with the fill hose routed through the cut-out area in the vacuum tank.

Pic 9

9. Attach the venturi assembly to the vacuum tank.

Pic 10

10. Attach a shop air hose to the venturi assembly.
Ensure the valve on the venturi assembly is closed.

Pic 11

11. Attach the vacuum hose to the vacuum gauge assembly and the vacuum tank.
12. Position the passenger compartment heater coolant control solenoid valve to normal using GDS. The hybrid powertrain control module 2 controls the passenger compartment heater coolant control solenoid Valve

pic 12

13. Open the valve on the venturi assembly. The vacuum gauge will begin to rise and a hissing noise will be present.

Pic 13

14. Continue to draw vacuum until the needle stops rising. This should be 610-660 mm Hg (24-26 in Hg).
Cooling hoses may start to collapse. This is normal due to vacuum draw.
15. To aid in the fill process, position the graduated reservoir above the coolant fill port.

Pic 14

16. Slowly open the valve on the vacuum gauge assembly. When the coolant reaches the top of the fill hose, close the valve. This will eliminate air from the fill hose.
17. Close the valve on the venture assembly.
18. If there is a suspected leak in the cooling system, allow the system to stabilize under vacuum and monitor for vacuum loss.
If vacuum loss is observed, refer to Loss of Coolant See: Cooling System > Symptom Related Diagnostic Procedures > Loss of Coolant.
19. Open the valve on the vacuum gauge assembly. The vacuum gauge will drop as coolant is drawn into the system.

Pic 15

20. Once the vacuum gauge reaches zero, close the valve on the vacuum gauge.
21. Repeat steps 14-21 one time.

Pic 16

22. Detach the Vac N Fill cap from the GE-42401-3 - Radiator
Cap and Surge Tank Test Adapter.
23. Remove GE-42401-2 - Radiator Cap and Surge Tank Test Adapter from the surge tank fill neck.
24. Add coolant to the system as necessary.
25. Turn on the auxiliary coolant pump for 2 minutes using the GDS. The remote HVAC module controls the auxiliary coolant pump.
26. Start the engine.
27. Using GDS, increase the speed to 2000 rpm until the thermostat opens (approximately 100C).

Note: Do not allow engine coolant temperature to exceed 110C or damage to the Coolant Heater Control Module could occur.

28. Turn engine off.
29. Turn on the auxiliary coolant pump for 1 minute using GDS.
30. Turn off the auxiliary coolant pump and wait 5 minutes.
31. Repeat steps 24-30, three times.
32. Inspect the concentration of the coolant mixture using GE-26568 - Coolant and Battery Tester.

Note: After filling the cooling system, the extraction hose can be used to remove excess coolant to achieve the proper coolant level.

33. Detach the vacuum hose form the vacuum gauge assembly.
34. Attach the extraction hose to the vacuum hose.

Pic 17

35. Open the valve on the venture assembly to start a vacuum draw.

Pic 18

36. Use the extraction hose to draw out coolant to the proper level.
37. The vacuum tank has a drain valve on the bottom of the tank. Open the valve to drain coolant from the vacuum tank into a suitable container for disposal.

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Let me know if this is what they tried.

Joe