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Discussion Starter #1 (Edited)
I have a 2006 G6 GTP Convertible with the 3.9L engine.
Ages ago I had a water leak (very typical of these engines - water pump gasket or crossover tube), fixed that. And googled around till I found the official air purge instructions from GM shop manual (since the 3.9L does not have a bleeder screw it is convoluted). Long story short, I need to purge it again, but no amount of google-foo of mine is finding those official GM shop manual instructions this time. I have seen all the regular old "typical advice" which works on most cars... the official procedure is very **very** convoluted and is the only thing that worked for me last time.


EDIT 2018.05.20 I found the proceedure and am reposting here for anyone who needs it - this is straight from GM in 2010.

1. Close the radiator drain cock.
2. If a complete engine block drain was required, install the coolant drain plugs
to the engine block. Refer to Draining Fluids and Oil Filter Removal for the
3.5L engine or to Draining Fluids and Oil Filter Removal for the 3.9L engine.
Important: Use a 50/50 mixture of DEX-COOL antifreeze and clean,
drinkable water.
3. Slowly fill the cooling system with a 50/50 coolant mixture until the coolant
level is visible and stable. Refer to Approximate Fluid Capacities .
4. Install the pressure cap loosely (threaded on about one turn).
5. Start the engine and raise the engine speed to 2500 RPM and hold it there for
40 seconds, then shut engine off.
6. Remove the pressure cap and fill the coolant system until the level is visible
and stable.
7. Install the pressure cap loosely (threaded on about one turn).
8. Start the engine and raise the engine speed to 2500 RPM and hold it there for
30 seconds, then shut engine off.
9. Remove the pressure cap and fill the coolant system until the level is visible
and stable.
10. Install the pressure cap loosely (threaded on about one turn).
11.Start the engine and raise the engine speed to 2500 RPM and hold it there for
20 seconds, then shut engine off.
12.Remove the pressure cap and fill the coolant system until the level is visible
and stable.
13. Install the pressure cap, fully threaded on.
14. Fill the coolant recovery bottle to the indicator line, then add 400 milliliters
(13.5 ounces) more.
15.Start the engine and run it above 2500 RPM until it is hot enough to open the
thermostat, this will allow the trapped air to be purged from the engine.
16.Complete a series of three, 4-second-duration idles with 4-second-duration
3000 RPM cycles.
17. Turn the engine off and allow it to cool down to room temperature.
18. Fill the coolant recovery bottle to the indicator line.
19. Inspect the concentration of the engine coolant using the J 26568 .
20.Rinse away any excess coolant from the engine and the engine compartment.
© 2010 General Motors. All rights reserved.
 

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Here's what both my manuals show:
I colored in RED the stuff not pertaining to your engine so you can just skip it

Fill Procedure
1. Notice: The procedure below must be followed. Improper coolant level could result in a low or high coolant level condition, causing engine
damage.
Install the engine block coolant drain plugs.
2. Close the radiator drain plug.
3. Lower the vehicle.
4. Vehicle should be level.
5. Add a mixture of 50/50 DEX-COOL(r) antifreeze and clean drinkable water until the level stabilizes at the weld seam on the surge tank.
6. For the 3.5L (LX9) engine only, unscrew the coolant bleed screw on the engine until coolant comes out of the bleed screw.
7. For the 3.5L (LX9) engine only, close the bleed screw.
8. Add coolant until the level stabilizes at the weld seam on the surge tank.
9. Install the surge tank cap.
10. Important: DO NOT exceed 2,200 RPM.
Start the engine and run at 2,000 RPM until the engine cooling fans turn ON.
11. Remove the surge tank cap.
12. Refill to the weld seam on the surge tank.
13. Important: Coolant should be at the full cold mark when the system cools.
Install the surge tank cap.
14. Inspect the concentration of the engine coolant using J26568. (Coolant tester tool)
15. Rinse away any excess coolant from the engine and the engine compartment.
 

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Discussion Starter #3
Thanks much for the info, can I probe just a little further on your source?.... Is that from a Chiltons or or... you say "manual" ... What I read so many months ago was a GM Shop Procedure Bulletin or TSB or something like that, can't find the same link again (spent another hour but my google-foo is still no-go) but it was definitely not just your generic for all models process found in the aftermarket manuals.
 

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That's the procedure listed in AllData and Mitchell onDemand.

I often help out at a buddies shop. Every cooling system he fills he uses a Coolant Vacuum Filler.
Whole system gets a vacuum pulled on it, then a valve is opened and the vacuum gets replaced with coolant/water
No where for air pockets to hide then. Simple test drive to ensure function and that usually is the end of it.


It also solved an overheating issue with my friends infiniti. Apparently an air bubble near the thermostat prevented it from opening and it would just overheat, After a vacuum fill the problem was gone. Later come to find that there's a bleeder valve on those engines.
 

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Apparently an air bubble near the thermostat prevented it from opening and it would just overheat
Sorry for resurrecting a dead thread, but I have had issues with my car's cooling system (Here) and after fixing and replacing what i believed to be my issues, I took it for a short putz around the neighborhood with no aparent issues, but today i drove took it in to work and on the highway it very quickly rose in temp up to just under the redline. I pulled over and checked to make sure all my coolant hadn't burst out again and it had not. I limped the car back home and took my truck in but I am wondering if something like what you described is happening to me. It seems as though the car will run all the way up to the redline and when stopped, it will creep back down, but if you go again, it will go right back to redline within 15-30 seconds. I don't have access to a vacuum fill system and am just trying to find a solution. I believe I likely over-filled the surge/recovery tank when filling it up and maybe that trapped air in the system. Do I need to go through that entire convoluted process above, or is there a relatively simple exploit to force the air out of the system after having just filled it up?
 

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Is your heater blowing hot?
So, went home did the steps above, took it for a test drive and I had the same problem where it just keeps getting hotter and then when I let off it cools down until I get on it again. So, I'm not sure what is happening but I would love some advice. Also, when I took it out again, yes it blew heat. Parts that I replaced were crossover pipe gaskets, water pump, thermostat. I have not tried the vacuum idea because I don't have one, and I don't know what to do from here. I'm wondering if maybe my water pump or thermostat that I bought are faulty.., but I have no idea how to confirm that without taking it all apart again and I definitely don't want to do that. Any ideas at all?
 

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When I changed my coolant, being careful of the fans etc., I vigorously and persistently squeezed/pumped the main hoses to the radiator. You should get waves in the coolant surge tank that will give you an idea that you are being vigorous enough. On mine I noticed a bit of a drop in the surge tank level which I believe indicated I had burped some air out of the system. I did this with the engine running and at normal temp to ensure the thermostat should want to open. I had the cap off of the surge tank when I did this to reduce any pressure.
 

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Don't mean to insult but...could you have installed the thermostat backwards ? The side with the spring needs to point at the engine.
 

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.could you have installed the thermostat backwards
I don't think it's actually possible to do this due to the shape of the thermostat housing. I don't think there's enough room inside that housing for the spring side of the thermostat to fit inside it.

Also, I just bit the bullet and bought a vacuum pump. I'll be testing it this weekend.
 

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I'll be very interested to hear about your experiences with the vacuum pump. - Mark
So, tried it today and I could get the too to create the start of a vacuum, but whenever I sealed the vacuum valve it steadily lost pressure and bubbles were coming up from my coolant line into the fill bottle. No amount of repetition would make this stop so I am wondering if I have an air leak. I have checked all over the engine bay and don't see any more coolant leaks, so I am unsure where else I could check. A friend said perhaps head gasket or intake, but then mentioned it shouldn't be the intake since it's a dry intake. Does anyone have any ideas?
 

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Apologies if you already considered that water boils at a lower temperature in the presence of a vacuum. Hopefully you tried this with the engine cold?

A known weak point is the "T" piece on the bottom of the hose that connects to the fill tank
 

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Apologies if you already considered that water boils at a lower temperature in the presence of a vacuum. Hopefully you tried this with the engine cold?

A known weak point is the "T" piece on the bottom of the hose that connects to the fill tank
Engine was not running. I have been told about the t-fitting, but it looks fine to me... I dunno, maybe I'll just replace it to be sure. Any part number or would a brass fitting from the hardware store work?
 

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Mine also looked fine but I was still slowly loosing coolant, probably only under pressure. I did get a replacement from an Ace Hardware store but I did not think to make note of the details. Mine was still plastic in the end. The brass one I brought was not snug enough at the time.

When I tried to remove mine it was so brittle it basically broke apart inside the hose and I had to pick lumps of it out with a screwdriver
 

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Well,
Mine also looked fine but I was still slowly loosing coolant, probably only under pressure. I did get a replacement from an Ace Hardware store but I did not think to make note of the details. Mine was still plastic in the end. The brass one I brought was not snug enough at the time.

When I tried to remove mine it was so brittle it basically broke apart inside the hose and I had to pick lumps of it out with a screwdriver
I guess I'll be checking that in a bit. Thanks! Sorry for the low effect reply here, the car is kind of breaking my spirit. I love driving it, but man... I just want to be able to...
 

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So, after performing the vacuum pump of the coolant system, I left the car alone because of the bubbles. But, last night I decided to just test it anyway and see what happens. So, I went through the motions, trying to replicate the overheating issue with no luck. I was pleasantly surprised and decided to take it for a test drive around 2 a.m.

It ran fine and I drove it around at highway speeds for about 10-15 minutes. It was at this point I decided that I was going to strain it and see what it can take because I am a spirited driver. So, I figured if I can make it hit the governor on an open and empty road and hold it there for a bit, that will be the most I ever do to this system and i'll be happy with it. So, I did just that, and pushed the car as hard as I could. The roads were completely empty and I was the only one at risk.

Anyway, I got it to the governor and held it there for about a minute before backing off, taking my exit, and heading back home. I checked the coolant level this morning before leaving for work and filled it to the cold-fill line since it had sucked some down into the system before the test drive. Drove it to work today and it did fine. I'm happy with it and don't really have any expectations for it to just crap out on me any time soon, so that's good!

Anyway, I just want to thank everyone here and on the other post that this whole journey started on. I really couldn't have done it without you all, but now the car seems to be in a stable, running state and I can rely on it. That's all thanks to you all and this great community!

Next up, Dyno test and exhaust swap for the coupe exhaust i got from the junkyard a couple weeks/months back to see if the exhaust swap can manage to bring the lost convertible horse-power back. I'll be posting numbers when I get them. Also, I guess I'll be putting all those suspension parts I bought on as well!
 
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