Gurgling heater core?

[steve75104]

On my '91 Chevy, the heater core sounds like it's gurgling when I start, stop, or turn a corner. Doesn't appear to be loosing coolant though and see no signs of leakage. Also checked pan under the core and it's dry. never any coolant in floorboard. Have recently replaced the water pump, all hoses, thermostat, and ensured the system is completely purged. Have also performed head gasket replacement and valve job (not associated with this issue). Any idea what would cause that sound and what might clear it up?

[lohanso]

No, but my 97 Sierra 4.3L V6 does the same thing .....

[dvreynolds]

You've probably still have some air in the system from the repairs, despite the purge. I think that, so long as the system reaches normal running temperature, air ought to gradually vent through the expansion tank. This works because the expansion tank stays at ambient pressure. Water forces its way past the radiator cap and goes in the expansion tank when the engine is warm, and retreats back to the radiator later on when the engine cools. As long as the tube in the expansion tank is below the surface, only liquid will return to the radiator. Any air that got out won't return. Trick is, you have to have the radiator etc. full or nearly so for this to work in the first place.
Gurgling and the like come from turbulence. I think that turbulence noise can be more with air bubbles in the mix. If you've got all your hose bends as smooth as before and the flow rate is about the same (and unless your water pump is on steroids) the system ought to be about as quiet as before.

[steve75104]

It was the drain tube for the air conditioining drain pan. Had been broken off and that causes a water backup. At least it's just a $2 part.... Thanks!