It sounds like radiator is working as they should ...because there is a drop in temp. between upper and lower hose...

But does that means thermostat is also working ...radiator is doing its job of lowering temp which is what we see in temp difference between upper and lower hose... but that does not prove thermostat is not stuck closed.. please advise

What other things you are referring to ...I think I have done everything else...and still doing...

It sounds like only reason I see bubbling coolant is head gasket problem...I have changed radiator cap...water pump ..thermostat gasket ..timing chain..anything should I check before I decide its head gasket or cracked head/block?

 

Here is my latest finding..

At idle at about 176 degree I opened the cap and check for hydrocarbons with combustion leak tester...liquid did not turn yellow ...I could not keep it for longer time because I was afraid coolant will start bubbling and steaming and overflowing...so I put the cap back on and at about 210 degree it did start bubbling and steam was coming out from that small hole on back of tank ...this continued to 219 which is when I turned off the engine...
So conclude if its head gasket at least it is not opening until 176 degree...(tech school instructor said ...it could be opening at higher temp because when he checked he could not find hydrocarbons either.

It sounds like thermostat is working and radiator is working ...

What else can cause this excessive pressure and lower boiling point ...
upper radiator was very firm ...which indicates excessive pressure..

cap is brand new...

Do u think something wrong with those or coolant recovery tank?

 

You can borrow a pressure testing system from places like AutoZone or O'Reilly's. With that you can test the cap and the system. Test when the system is cool. Pressurize it and see if it holds pressure over time.
If not, then you'll need to find the leak. We previously mentioned the dye.
The LAST thing you want to do unless you are absolutely certain is replace the head gaskets. It's VERY expensive. Do ALL the cheaper things first. If you paid a couple of thousand dollars for head gaskets and then later found out it was something cheap that cost $10 to fix, you'd feel like an idiot for the rest of your life.
Pressure in the system is determined by the radiator cap. It should be about 15 psi. You can't have excess pressure in one part of the system. It will be the same throughout. Laws of physics. Likewise, the laws of physics say that the higher the pressure, the higher the boiling point. IF you have excess pressure, you won't have a reduced boiling point. If you have air in the system, you will see bubbling at lower temperatures as the air expands while the engine is warming up.

 

1. I believe when they changed thermostat gasket and water pump ...leaks are sealed ...I dont see any visible leak on the ground but I understand that does not mean there is no leak....
2. Another interesting thing I notice that when coolant was bubbling inside the tank ...there was some liquid movement in ac low port point...does it mean anything?

3.If I have higher pressure than higher boiling point ...I understand that...so you are saying I see bubbling because I have air in system? but this air can be due to head gasket opening up at higher temp or something else?

4. You said run few cycles and air will be burped automatically...what exactly should I do ...let it run until it bubbles and than turn off and do it again ..how many times?

5. Yes I will check with pressure tester and post results

 

Previously, you said you had seen leaks on the ground, apparently not now. Leaks can still be small and not reach the ground. The point is that if there is a leak, coolant can leak out and air can leak in.
When every other possible cause of your overheating, bubbling has been ruled out, and a head gasket problem has been confirmed with the necessary testing, THEN, if you still want to invest that kind of money in this 13- going on 14-year-old car, then you can do whatever you want. Cross that bridge when you come to it. You're still not even close.
If the system is working properly, air will work its way out after a few driving cycles. We've been over this. I recommend you go back and read through all your threads on this subject from beginning to end.

 

NO leaks on ground...or anywhere that I can see...

You said earlier and now that drive cycles will burp air out if its trapped..

But I cant drive this car...because its starting to spit out coolant after few minutes of drive in neighborhood....that is why I asked what should I do to make sure air is burped out...

Ofcourse if it has leak air will be sucked in and we cant burp air out ....

I dont want to spend money and time on head gasket that is why I am trying to figure out what else is causing this bubbling or overflowing form tank...

It looks like either head gasket/ cracked head or leak somewhere ...I am trying to figure out where leak is if any.

 

Remove the topmost hose on the coolant outflow manifold as you fill the system with coolant. It's very close to the bleeder valve and if you can fill to that level there should only be a teaspoonful of air left in there. Not enough to worry about. Don't touch the bleeder valve. It was put there for use in the assembly plant, ONE TIME, when they filled the car with coolant at assembly. After time the threads seize and if you try to do it again the chances are very good that you will spin the thread seat in the plastic and cause a leak. Since it's the top-most point in the system, air can leak in and cause problems.

Action plan: Get cooling system pressure test set from auto parts store on loan. No need to buy it. Test system for leaks under pressure. If loss of pressure is observed over time (hour or two), get dye to pinpoint location of leak unless you can see it while the system is under pressure.

 

Is there any connection with AC system and cooling system internally? I mean can anything wrong in AC system can cause leak in cooling system and could cause excessive pressure low boiling point and overheat ...I am asking this again because
I noticed that when coolant was bubbling inside the tank ...there was some liquid movement in ac low port point...does it mean anything?

 

The AC and cooling systems are completely separate. There's no way coolant can leak into the AC system or vice versa. Both dcotter and myself have recommended that you get a coolant pressure tester but you keep ignoring our suggestions. That's the only way you will know sure if you have a leak. Everything else you've mentioned is just grasping at straws. Until you decide to troubleshoot your problem using common sense techniques I can't help you any further.

John

 

With your temp gun, check the temps throughout your radiator. Check for possible blockage.