Purging air from cooling system/Odd idle?? *urgent request*

[CarneySC]

Hello guys! I've been reading through your forums from the Google responses, and decided to just sign up, and ask the question my way. So, here goes:

I have a 2005 Trailblazer LS, with a Vortec 4.2 ltr I-6. I just replaced the thermostat yesterday (which, was loaaads of fun), and now, with the new thermostat in, it's retaining air. I've tried bleeding the air from the system by running it in idle with the cap off the radiator for over a half hour, and still there's an air bubble somewhere. Once it gets up to heat, the new thermostat also won't open. Looking through my Haynes manual, it says there is a air line connected to the Throttle Body that may be used to bleed air, but my question is...WHERE? Not one single site have I found has a clear, concise answer to this. Furthermore, the idle is off as well. It will idle perfectly, then it gets to normal operating temp, and it wavers from normal idle, to a reduced idle, like there is a draw on the engine.

SO, to organize my questions:
1. How in the deuce do you purge the air OTHER than the radiator cap?
2. Where is this air bleed line that the manual says is connected to the throttle body?
3. What is the reason for the fluctuating idle?
4. IF there IS no bleed line, why will it not bleed the air through the cap?
5. HOW do I bleed the rest of the air?
6. Why won't the new, out of box, thermostat open when it gets to the right temp?

PLEASE respond soon, this is an urgent matter, as I've college, and various doctor appointments to attend tomorrow!

 

[meerschm]

I have a 2005 Trailblazer LS, with a Vortec 4.2 ltr I-6. I just replaced the thermostat yesterday (which, was loaaads of fun), and now, with the new thermostat in, it's retaining air. I've tried bleeding the air from the system by running it in idle with the cap off the radiator for over a half hour, and still there's an air bubble somewhere. Once it gets up to heat, the new thermostat also won't open.

How do you know this?

Looking through my Haynes manual, it says there is a air line connected to the Throttle Body that may be used to bleed air, but my question is...WHERE?

on the V8 you don't have. the I6 does not have this.

Not one single site have I found has a clear, concise answer to this. Furthermore, the idle is off as well. It will idle perfectly, then it gets to normal operating temp, and it wavers from normal idle, to a reduced idle, like there is a draw on the engine.

SO, to organize my questions:
1. How in the deuce do you purge the air OTHER than the radiator cap?

after running a bit with the cap off, should be ok

2. Where is this air bleed line that the manual says is connected to the throttle body?

On the V-8 engine
3. What is the reason for the fluctuating idle?

have you cleaned your Throttle body intake? could be dirty and, assuming you had the battery disconnected, could have reset and not learned how to compensate for dirty opening.


4. IF there IS no bleed line, why will it not bleed the air through the cap?
5. HOW do I bleed the rest of the air?
6. Why won't the new, out of box, thermostat open when it gets to the right temp?

could be bad. could it be the thermostat is not sealed? or perhaps the old o ring is jammed into the works of the thermostat. if you warm up engine with the rad cap on, does it leak?

 

[meerschm]

SO, to organize my questions:
1. How in the deuce do you purge the air OTHER than the radiator cap?
2. Where is this air bleed line that the manual says is connected to the throttle body?
3. What is the reason for the fluctuating idle?
4. IF there IS no bleed line, why will it not bleed the air through the cap?
5. HOW do I bleed the rest of the air?
6. Why won't the new, out of box, thermostat open when it gets to the right temp?

!

1. How in the deuce do you purge the air OTHER than the radiator cap?

that should work.
2. Where is this air bleed line that the manual says is connected to the throttle body?
that is on the V8


3. What is the reason for the fluctuating idle?

could be dirty throttle body.

4. IF there IS no bleed line, why will it not bleed the air through the cap?
should do this over time

5. HOW do I bleed the rest of the air?

if you park a bit headed uphill, and run for a minute or two with the rad cap off, you should be ok rest will work out coolant recovery tank.

6. Why won't the new, out of box, thermostat open when it gets to the right temp?

how do you know it is not working?
it could be bad, or jammed.

how do you tell it is not working? do you have a way to read the temp from the OBD?

do you have a check engine light?

 

[Wooluf1952]

Welcome


In case you haven't heard:
http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/


If the t-stat doesn't open the engine will over heat. What does the thermostat read?

As for the air bubble, I can only relate what happened to me:

January 2008, I replaced the coolant and only had to add a small amount over the next few months as the air purged out. The level never changed until....
March 2011, I came home from a two week vacation and the over-flow tank was empty. Nothing on the floor of the garage. The coolant was just gone.
March 2012, I made sure to check the coolant in the over-flow reservoir was right at the hot level where it was supposed to be. Went on vacation again for two weeks. Got home, checked the coolant level, and again the reservoir was empty.
So in two years I needed to add one gallon of coolant.
This past March the reservoir was full when I got back.
The truck is parked with the front end slightly higher than the back, so the only thing I can think of is the engine purging out the air over a 4-5 year period. I'll check again next vacation, but if anyone has a better explanation, I'm listening.

 

[AbsoluteZero]

Some thoughts ....
If you disconnected the battery to get the alternator out of the way when changing the thermostat (which I would hope you did), the vehicle's computer (PCM) will think you have a clean throttle body, among other things. If the throttle body is dirty as suggested a cleaning may correct your idle problem.
I've changed the t-stat 3 times on my 03... never had an issue with bleeding air from the system. A couple cycles of hot/cold and the coolant reservoir stays at the same level.
Before installing the new stat assure it opens in boiling water. Occasionally a new t-stat is bad out of the box.
I apply a thin bead of RTV to hold the o-ring in place. It's in a blind area and, as mentioned, if it gets out of place it can interfere with the t-stat's operation.
Also it's been recommended to replace the engine coolant temperature sensor that's adjacent to the t-stat when replacing the t-stat. With time the sensor "ages" and can give an erroneous reading.
If your radiator cap is bad it may not allow air to bleed out or fluid to be sucked in from the reservoir during the hot/cold cycle.
With the above info and less than a dollar you can get a senior coffee at McDonald's most days!

 

[eXplicit]

I don't mean to throw a huge detour in your search for an answer here, but I just recently had the same problem with my 02 LTZ. Except mine was overheating. It would not stop bubbling. Had it checked, and it wasn't air from the cooling system, but instead it was actually combustion gas coming from the cylinders, which was the result of a warped head. I'm still putting the thing back together. I would get a test kit and make sure it's not combustion gas from the cylinder head or gasket.