How Can I Purge Air Out of Radiator ? - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 23 (permalink) Old 12-23-2012, 01:59 PM Thread Starter
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How Can I Purge Air Out of Radiator ?

Hello All,

I just signed up as I am having some issues with my wife's 2008 Cobalt LT.
It has 86K Miles, everything runs fine its been overheating lately.

It used to be stable at 189 F, but it started goin up to 200's, 210's up till 230 specially when going up hill, weird part if im going down hill it drops 20 degrees within minutes

I Investigated and I had low coolant level, filled it up, it kept fluctuating from 189 to 200's this time. but it was running with no overheating issue any more. However a friend said it could be a bad thermostat with fauluty reading and suggested i replace.

He swapped it out for me, and while replacing he drained the anti freez (dont know if he is supposed to do that, anyhow, he was able to put in the new thermostat, and filled the car with dex cool halfway and the rest with water as we didnt have much.

now the car is worse, its overheating badly it even went up to 250F and kicked in cooling mode. He assumes there is air trapped.

How can I purge the air out from the system ? is there a better solution? What wronge did he commit?

I appreciate everybody's help and input!
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post #2 of 23 (permalink) Old 01-02-2013, 02:17 PM
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First off I would suggest to get rid of the water you put in. Water has a much lower boiling point. Unless the dex-cool specifically says to mix in. It should say DO NOT MIX WITH WATER on the bottom if it was the 50/50. As for the question you had. You need to open the cap when the engine is COOL to the radiator and run the car with the heater on. Let it warm up for a while and that should do it. But for starters check the bottle of the dex-cool. -Puddle
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post #3 of 23 (permalink) Old 01-02-2013, 02:23 PM
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You absolutely should not add water to a Cobalt's cooling system, especially if you are using Dexcool.


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post #4 of 23 (permalink) Old 01-02-2013, 02:27 PM
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Changing the thermostat might have been premature. These cars will give you a code when the thermostat goes bad. Plus with these car when the thermostat goes bad you will get the opposite of your symptoms where the engine does not reach operating temperature of 194F.

This is all normal, when temperature reaches a predetermined value fan or fans come on and bring temps down then shut off until temps reach these value again. The two fan speeds are determined by coolant temperature. The PCM commands Low Speed Fans ON under the following conditions:

Engine coolant temperature (ECT) exceeds approximately 106C (223F).
A/C refrigerant pressure exceeds 1 310 kPa (190 psi).
After the vehicle is shut off, the ECT at key-off is greater than 140C (284F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans ON under the following conditions:
ECT reaches 110C (230F).
A/C refrigerant pressure exceeds 1 655 kPa (240 psi).
When certain DTCs set

https://www.yourcobalt.com/forums/eng...highway-2.html


---------- Post added at 05:27 PM ---------- Previous post was at 05:25 PM ----------

Dexcool comes in both variety, the 50/50 premix and the concentrated version you add water.

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post #5 of 23 (permalink) Old 01-02-2013, 02:36 PM
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^Good to know


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post #6 of 23 (permalink) Old 01-02-2013, 03:46 PM Thread Starter
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THanks everybody for your input,

What has happened since, is I poured more anti freeze via hose and that pushed fluid back in overflow tank.

now that car drives fine and reaches 210's when driving in city.

Weird issue is when I hit the freeway it will surge to high 230's, 240's

there is still water / dex cool in the system and I dont know if that is affecting and has to be drained.

I have been told there might be bubbles still and it has to be bleed properly via bleeder valve...

What do ya'll think ??

thanks everybody

Last edited by Coby7; 01-02-2013 at 03:58 PM.
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post #7 of 23 (permalink) Old 01-02-2013, 03:53 PM
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I suggest doing it via radiator cap. Like I said at the top. But getting that water out is a must. Click the link below.
https://www.yourcobalt.com/forums/pro...alve-2-2l.html
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post #8 of 23 (permalink) Old 01-02-2013, 03:56 PM
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No bleeder valve on Cobalt. Like previous post says, from cold start remove radiator cap, turn heater on to lowest fan position let run until thermostat opens. Any air in the system will be forced out to the radiator and levels will drop. Then put cap on let run for a couple of minutes then top up reservoir. Keep an eye on it for a couple of days.

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post #9 of 23 (permalink) Old 01-02-2013, 03:57 PM Thread Starter
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I might be wrong, but when I opened up the hood and pulled the plastic coverings I didn't a radiator cap.
all i saw was the Over flow tank
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post #10 of 23 (permalink) Old 01-02-2013, 04:03 PM
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No you might be right and I'm wrong. Same principal though.

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