bubbles in coolant reservoir???
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yes, i just got the replacement today , i installed it and also installed a new cap and Burped the system. Tomorrow when she is fully cooled down i am gonna do another pressure test to double check everything
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hey folks, I got 2007 hummer H3 around 135k miles. recently all the sudden I been having bubbles coming from the coolant reservoir and overheating like 220+. and when I drive on it, the coolant in the radiator is low but the reservoir still full. I did a chemical block test for blown head gasket and it came negative, no leak visible anywhere outside, no white smoke from exhaust and no mix coolant with oil. I did a pressure test and it's not holding pressure when I go 15PSI, it immediately start to go down slowly while bubbling coming from the coolant reservoir. I changed the thermostat thinking it's maybe not opening but still the same problem.. anyone knows what's going on? is it a bad head gasket???
thank you
thank you
Sadly i still have a problem. When i do. A pressure test it’s fine but when i took it for a drive! I noticed the hoses are like very hard and alot of pressure in the radiator you can till
from how swollen is the hoses. It’s brand new radiator and brand new cap. Does that mean it’s a head gasket bad? Leaking gases into the coolant side and causes the pressure to increase!? Or is it possible my water pump?
i dont know what else i could think of beside that
Last edited by NFS; Sep 28, 2025 at 07:28 PM.
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Joined: Jul 2007
Posts: 13,101
From: Boat Town USA MI
What condition are your Cooling Hoses in? They are 18 years old if still OEM.
Is your T Stat opening and closing properly? I had to replace mine on the old 07 as it was stuck open and triggered the code for too long to reach operating temp. Yours could be sticking closed.
Is it your original water pump? We know how old that is too.
Is your T Stat opening and closing properly? I had to replace mine on the old 07 as it was stuck open and triggered the code for too long to reach operating temp. Yours could be sticking closed.
Is it your original water pump? We know how old that is too.
Thread Starter
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Senior Member
Joined: May 2016
Posts: 739
What condition are your Cooling Hoses in? They are 18 years old if still OEM.
Is your T Stat opening and closing properly? I had to replace mine on the old 07 as it was stuck open and triggered the code for too long to reach operating temp. Yours could be sticking closed.
Is it your original water pump? We know how old that is too.
Is your T Stat opening and closing properly? I had to replace mine on the old 07 as it was stuck open and triggered the code for too long to reach operating temp. Yours could be sticking closed.
Is it your original water pump? We know how old that is too.
the hoses are like 2 years old and so as the water pump
the T state I changed it 1 months ago
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Senior Member
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I have that already and I did it few times even when it was bubbling I did it and it keep coming negative
Senior Member
Joined: Apr 2019
Posts: 3,207
From: BX NY North East
are you running 50/50 or water? water boils over quicker then 50/50 even under 15 psi of pressure. im guessing thats what a stock coolant cap is. water boils at 250F under 15psi of pressure. 50/50 boils at about 270F. either way those temps are pretty destructive.
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I am running 50/50 dexcool orange coolant . I even flushed it and put brand new coolant when I installed the new radiator
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Joined: Apr 2019
Posts: 3,207
From: BX NY North East
if it is holding pressure and your not detecting combustion gasses in your coolant then you probably have a massive coolant bubble trapped in the head or head flow is being restricted for some reason. clogged passages around the cylinder ports? have you used some sort of block sealer in the past before the issue you have now?
does the clutch fan feel nice and tight to turn?
does the clutch fan feel nice and tight to turn?