Water bubbling..

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!!

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

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?

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?

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

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

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

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?:banghead:

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.

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.

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

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. :banghead::banghead:
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??

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.

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

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?

I believe the thermostat is pressed into the pipe. That's why they sell it as one piece. But I think your mechanic buddy may be right about your radiator. If by feeling the radiator you have hot and cold spots. The passages may be partially plugged. Just cause you can flow water throw with a hose is not a good test.

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.
The radiator flows from top to bottom, just like it's 1966 again. Cross-flow radiators became almost universal for awhile, then GM goes back to downflow on the Trailblazer radiators for some silly reason. Yes, the radiator will be hottest at the top, and cooler as you go down to the lower rad hose.

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.
Not sure that's accurate. I thought the thermostat was on the inlet side of the water pump--backwards from "normal" practice.

I'll have to dig through the shop manual to see what's up with that. It just seems really screwy.

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?
I suppose you could rip the thermostat out of the pipe...but it's not intended to be removed. Companies make more money when they can sell the entire housing instead of the $5 thermostat. You'll be buying a new thermostat/housing assembly if you remove the thermostat from the housing you have.







Are you having any problems with the thing running? If you drove it for two hours, would it be boiling over with you stranded on the side of the road?

What is the anti-freeze concentration?

Are the fins of the A/C condenser folded-over, or filthy? When I replaced the fan clutch on my Trailblazer, I blew compressed air backwards through the radiator fins and the condenser fins. I was really surprised at how much dirt was hiding in the air fins.

So I took off the valve from thermostat pipe, it's easy once you have it in your hands.. and you can put it back on engine empty as a test. I will drive it next days and see what happens. To help people who will attempt thermostat replacement in the future, this is what I did:
- make sure you have no hurry and some beers off the shelf to keep you calm
- you father in law helping..
- take off belt
- take off negative battery pole for safety
- loose all three alternator bolts without removing it
- jack car and take off front left wheel
- reach bottom thermostat 10mm bolt from left coil side, easy
- reach top thermostat 10mm bolt from left coil side. Alternator has to move forward and leave some room to do this. You also need a custom key rod really long to reach this bolt I suggest 1/4" size
- once thermostat is loosen if you pull and bend hose from the battery housing with some patience, you can have it in your hands and in front of your eyes, remove clamp and replace it. When installing the new one make sure to put it in the right direction as the old one.
- have a beer
- good luck for next steps of this tricky job!

I really hope this was my problem but I will know next days. I will buy a new thermostat and put it back on. Hope is not head gasket, head cracked or what... who knows?? Cross my fingers and go..
Every time I have to open hood, I ask myself why the hell I sold my old 5.2 grand cherokee, I really miss it. This car is a pain.

Took off old thermostatic valve but temperature doesn't raise, not a great test. Need a new one. Would you get a gm for 140 euro or a doorman sent for 50 bucks? Italian prices, not cheap I know.
Thank you

Hi. Just as feedback, this was the thermostat that used to stuck half way.. thank you all.

Hi together,
When I drive by car (Audi A6), the car starts to vibrate after 15 minutes and when I stop, the water starts to bubble.
can you tell what the problem can have my car?
That will help me.
Thanks

You need to post this in the Audi forum, this is Chevy trucks.

Oh, thank you for information.
I'll do it.