Hi all posted this in another forumn on here no replys so ill try in here.\


i have a 2007 v36 sedan low mileage 64000 km
Out of the blue i heard air bubbles behind the dashboard after starting up,i lift the hood and see the coolant tank rather full,so immediatly you think head gasket,well i did.And with cap off i see big bubbles coming up not the fine ones i was expecting.
So off to the mechanic he pressure tests the cooling system no problem found so he suggests throttle body off for a leak down test and compession test on all these test nothing found to suggest head gaskets.
where can these bubbles come from? its got him a bit stumped He did say its a possibility for the water pump to suck air in,anyone seen this?
I have no water in oil and no oil in water,the car runs fine.

Thank you for taking the time to read any ideas would be great........phil

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It would have to be something that is high up on the motor or the component that is allowing the air in would be leaking. A failed water pump seal can lead to bubbling so that is a possibility. If HG issue are you seeing coolant mixed in the oil or white smoke?

No oil in water. No water in oil. I don't recall white smoke. But have now marked reservoir to see if any is going somewhere… I just got hold of a co2 tester and bubbles didn't show co2 present .
Thanx for reply

I have seen some indicate that bubbles can be pulled into the system via a bad radiator cap as well. Something to look into.