Air bubbles in cooling system


Veteran Member
Jul 22, 2014
Gardner, KS
Gm released a TSB for these cars for air in the cooling system. They have a specific procedure of running, shut downs, re running, to get it all cleared out. Most of the time the complaint is poor heat output when this happens. Im not at work so I cant look up the specific procedure, but if I remember right you screw the cap on 1 turn, and run it at like 2000 rpm for 3 or 5 min. shut it off for 1 or 2, top off coolant, put cap back on 1 turn again, run it another 3 to 5 for 2500 rpm, shut down for a 1 or 2 min, top off coolant, 1 full turn on cap, then go 3000 rpm, again, after that top off screw cap on fully, should be good to go.

IF its not overheating don't worry about the small bubbles. Ive seen random newer cars doing it, but they don't have anything wrong. I think some of it may be cavitation of the water pump, which gets dissipated with radiatior cap pressure.

Hope this helps


Veteran Member
Lifetime Gold Member
Aug 29, 2007
Western, MA
I think you are over thinking this. Are you getting white smoke out the back and does it smell sweet?

Does the oil have any signs of moisture in it? Milky or milky dipstick?

You already said you are not losing any coolant.

Did you drill a little 1/8" hole in your thermostat rim to let air pass through?

I say drive it and see if the symptoms get worse. If you are that concerned run a compression test and make it certain.

ol' grouch

Veteran Member
Jul 4, 2013
Evansville, In.
If the head gasket is blown or the head is cracked, it's blown or cracked. If not, you're probably getting trapped air out a little at a time. Newer engines can be bears to purge. Since the 90's, engines, especially the GM engines, tend to hold air. There are bleeder valves, often in hidden and odd places to get the air out.

You can borrow a tester at Autozone to test the pressure. That would be the way to go. If the pressure stays constant when warmed to operating temperature, you're good to go. If the pressure keeps increasing, especially if you're getting a lot of bubbles, you need to decide how to deal with a blown head gasket.

Personally, I think if he pulled over and shut it down as soon as possible, it may just be trapped air.

76 camaro car 1

Veteran Member
Apr 23, 2010
There is no bleeder valve on the 3.9 unfortunately. Took it on another 20 mile ride last night. I rechecked the coolant this morning and it is still full. I think it is just trapped air. I will try the procedure suggested by camarolife 78 and see if it works. It lost about a quart of coolant when it blew the hose and was then filled with water so my son could drive the car about a 1/4 mile to his friends house. I had the car towed back home and drained even more coolant so I could get close to the 50-50 mix. So it had probably 2 quarts of new coolant and water replaced. That I guess could leave a lot of trapped air. I just do not want my son or daughter to get stranded late at night with the car.


Veteran Member
May 27, 2006
As mentioned it could just be trapped air bubbles. I own a 91 Toyota with a 22re engine and it's difficult to get the air bubbles out because of the way the hoses are routed. Air bubbles in that system cause erratic engine operation because of the sensor placement. Part of my success is to get the radiator opening as high as possible to help drive out trapped air. I then raise it higher with a purchased funnel/filler. Lisle No Spill Funnel

Just one example of how to use it.

The procedure that has worked the best for me is to
First set the coolant in the overflow bottle to its correct height.
Jack the front of the vehicle up as high as I can and place it on jack stands.
Set the heater temperature selector on full hot and leave the blower fan off.
(I'm not sure where your actual heater control VALVE is located but you should verify that it is fully open)

Remove the radiator cap and install the Lisle No Spill Funnel.
Add a little water/coolant so I can see a little liquid up top.
(That way I can see water moving when the thermostat opens and closes)
Start the engine.

When the thermostat is finally doing it's job and the temperature finally stabilizes you rev the engine and squeeze the hoses and if there's any trapped air you can see it bubble in the Lisle No Spill Funnel.

If you think you have a combustion chamber leak there is a specific tool that will check for actual combustion gasses leaking into the cooling system. When the combustion gasses interact with the liquid in the tester the liquid changes color indicating a leak. One of the cheaper ones
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