Hello there!

I hear a bubbling noise which appears to come from the heater core. Sounds like there is air in the system. Never heard it before. It happens at about 2-3000 rpm. The car is heating normally, I checked the coolant level and it appears normal, no leaks. Could this be the monovalve stuck open?

Thanks

Vlad
87 300 TDT 415,000 km

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Vlad B
Toronto Ontario

1987 300 TDT 415,000 km
on B20 since 2005; on Mobil1 since 2004