Water bubbling..

[chiccokaiser1]

Hi everybody. I already took a look to threads concerning this issue but I need to ask something:
- 2002 ltz 4.2
- Bubbling happens in big top radiator hose when I turn off engine
- Water pump just replaced
- 225000 km engine
- No water in the oil, no oil in the water
- Engine temperature always perfect
- Just flush cooling circuit with a bardhal cleaner but radiator is very hot at the top where I can feel bubbling, cool the rest
My buddy mechanic says to replace radiator but water seems to go through easy if I disconnect both hoses and let water drop inside by a garden hose..
So what could be next? New radiator or head gasket?
Thank you!!

[Tech II]

You have opened up the system, since it is not overheating, it's possible it's not completely burped of air....

[maxwedge]

Do you mean you hear bubbling, did you bleed the cooling system properly, could be air trapped. I had the same truck, never was happy with it, ok, this started after the water pump job, no?

[chiccokaiser1]

I am not that lucky usually... I wish it has just to be purged..

By the way, all the job started due to bubbling so I guess in that time system was purged properly, nobody touch the engine until now.

What about purge it? Is there a procedure or shall I just drive and wait for reservoir tank and radiator cap doing their job?

[chiccokaiser1]

I forgot, I also replaced radiator cap with a new ac delco one.

[aleekat]

Park it nose uphill. Remove rad cap. Put heater on full. Run the car.

[chiccokaiser1]

Ooook, let's try then. I'll write back.
Thanks

[chiccokaiser1]

Not lucky, even after cooling system bleeding engine still bubbles. Reservoir tank was a bit under pressure also..
What do you suggest? New radiator or straight to head gasket?

[Blue Bowtie]

If the cooling system is generating bubble while running (with the cap removed) it's a good bet that there is a compression leak somewhere.

[chiccokaiser1]

It actually bubbles when I drive it for at least half an hour, as soon as I turn off the engine. Radiator it's not hot everywhere but mostly at the top close to the inlet hose. Going down with my hand i feel it gets cooler but I don't know if this is normal (due to fan) or not.

[chiccokaiser1]

Replaced radiator and still no result. I guess now head is coming off.. what do you think?

[chiccokaiser1]

My mechanic took a look deeper and I was told to try to take out thermostat but I have seen it is underneath and not on the head.. lost my time tonight.
I will keep working next days but in the end it make sense.. if thermostat is after radiator in water flow it could be the cause of my defect.. ain't it??

[aleekat]

Just because it is lower does not mean it is flowing the opposite direction. It may be a thermostat issue. But the coolant heats in the engine until the thermostat opens flowing into the radiator and back through. Look on Youtube. Bunch of thermo replacement videos for your trailblazer.

[chiccokaiser1]

Thanks.. I will look right now. I don't work in a garage but I have never seen thermostatic valve on the engine block..

[chiccokaiser1]

Seen a video.. not a fun job.. The guy replaces it with a new one but I would like just to take valve out as a test. Do you know if old thermostat comes off the alu pipe and I can still put it back on with its O ring but as an empty pipe?