Bubbles in coolant

2008 uplander with the 3900 in it. I have bubbles in the cooling system that never seem to go away.
My initial suspicion was combustion gasses but I did a test for combustion gasses and it came up negative (I retested and retested and retested…). Test indicator fluid is good. System has been filled, burped, brought to temp, front end raised, filled again, burped, and so on. Levels don’t seem to drop, but time will tell I suppose. Coolant is getting displaced into overflow and sucked back in when it’s cool. System is not leaking (held a vacuum).
Short vid of the amount of bubbles I see when engine is warm at idle: bubbles in coolant 2008 Chevy uplander 3900 - YouTube
Note that if you leave it idle for a long time the bubbles will almost stop. But if you increase the RPM a little you’ll get them moving again.
Head gasket even though the test says no?

try replacing the radiator or overflow bottle cap.

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Sounds like a head gasket leak to me. Some bubbling after first starting the engine is normal b/c air can get trapped in thehose between the radiator and the overflow tank as the engine cools, which will create bubbles as it heats back up again upon restarting the engine. But if you’ve waited until the bubbles stop (usually that’s only a minute or two), and then the bubbles start again when reving the engine, that’s not a good sign.

Have you ever had any overheating incidents?

No overheating that I’m aware of under normal conditions - thermostat appears to open at 190, system will go up to a max of 227 then the fan kicks on and drives it down to 210, and those temps seem to be in line with what’s expected.

I didn’t do the cap yet because it pushes the coolant into the overflow and sucks it back properly, but that’d probably be good to throw a part at and see.

Bubbles continue after it’s run for a while (>10 min, probably >20 min even). Slow, but present. Revving generates more. IMO the car isn’t worth the expense of a head gasket.

Last uplander I had (2005) had the same issue. I did a hail-mary and used some of that magical “gasket fix” stuff that I was sure would not work. I followed the directions exactly and indeed, it did not work. In fact it gummed up the system so bad that between that and the head gasket, I scrapped it.

Yes, but with no detected exhaust gases?

I might try and find a shop that would do a vacuum purge to pull out air bubbles, after they did a pressure test to see if there were any leaks.

I see a purge/pressure test kit on Az for 90$. I think I’m over my tool budget this month but maybe I’ll get one and try it. Burping cooling systems is always such a PITA so it would be nice to no longer have that problem at least.

I owned a truck several years ago that had bubbles similar to that, but maybe slightly smaller bubbles. I never had any overheating or anything. Bubbles would increase as you revved the engine also. I had about $600 in the whole truck, so I just ignored it and stopped staring into the radiator at idle! I think I put around 10k miles on it and eventually sold it.


One of the experts here – I think it was Nevada – mentioned a while ago that in his experience a “passing” score on a coolant chemical test doesn’t necessarily imply a fully continent head gasket.

I wouldn’t trust the chem sniffer for a turd’s worth.

Bought it used? Possible somebody else cracked the head and did a seal?

My experience: if the bubbles come up in small bursts at consistent intervals at idle, you are hosed. Otherwise, it could be air getting sucked in from some small leak.

Also, if revving the engine momentarily pulls the coolant level below the radiator coils, you’ll get air.

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That’s what my gut’s telling me. Chem sniffer is 1st hand, but from Harbor Freight. I tested the fluid on the real exhaust pipe and it immediately went yellow. Instructions say to suck air from the coolant system for 1min - I did 2+ min with no detection. So it’s a matter of sensitivity I suppose. I’d wager it does have a HG leak but it’s quite small at this point. Cooling system on this car sucks as it pulls coolant back and forth across the engine bay for no real reason other than maybe being able to use an existing radiator and the thermostat is buried. Another hooptie to drive into the ground I guess. A Michigan car - it’s not like the body is going to last.

It does indeed pull down quite far on rev. Could be that’s all it is. I’ll cross my fingers and hope for the best. When it starts overheating and gushing air I’ll know it’s time to retire it.
Thanks for all the information everybody - really appreciate the input.

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