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#2105977 - 12/14/10 04:48 PM Procedure to bleed air from thermostat on 3.8L GM
BLJ Offline


Registered: 08/03/08
Posts: 25
Loc: Alabama
i replaced my water pump on my car and now the engine takes forever to get to 140 F. The heater is luke warm air. Could it be air in thermostat housing causing the thermostat to stay open. The theromstat was replaced 8 months ago with a Can't Fail thermostat which will fail in the open position. What is the proper procedure for bleeding the air with the valve on the top of the thermostat housing.

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#2105986 - 12/14/10 04:55 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
Steve S Offline


Registered: 01/20/03
Posts: 18449
Loc: East of IGO
With the engine cold loosen the top radiator hose where it connects to the thermostat housing. just enough to let the air if any out. If that is the problem. What brand ot t stat did you install?
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#2105990 - 12/14/10 04:57 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
beast3300 Offline


Registered: 12/24/09
Posts: 3033
Loc: Ohio
Open the bleeder on a cold engine, add as much coolant as it will take through the radiator. Close bleeder. Run engine and add to radiator as necessary while it warms up.

Install cap, allow to build pressure and get up to normal operating temp. Open bleeder while running at this point. It should "pee" coolant. When it does just re-tighten bleeder and verify heat.

You may have to shut it off for a little bit to build pressure. Maybe 10 mins. Then open cap and add until full. Recap it and that should get 95% of the air.
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#2106003 - 12/14/10 05:06 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
Trav Offline


Registered: 11/20/06
Posts: 10264
Loc: MA, Mittelfranken.de
I have been reading about these things failing in the open position.If bleeding it brings no improvement its a good chance its failed.Buy an OEM unit from the local GM dealer!
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#2106019 - 12/14/10 05:20 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
eljefino Offline


Registered: 06/15/03
Posts: 24432
Loc: ME
Usually the thermostat sits in a gooseneck slightly downhill from the top radiator hose which is all full of coolant.

You sometimes need to burp air when they're brand new, to get around the catch-22 of a closed thermostat air lock not letting coolant activate it. Once activated the air gets to the radiator, cap, and overflow tank where it bubbles out. Some thermostats have tiny built in leaks like jiggle pins that help with this. You may also be able to back-fill the system through the vanes of the water pump, but perhaps not if they're new and "tight".

Are you positive your water pump is actually pumping? Can you feel water running if you fiercely squeeze the top rad hose? Can you drive 20 miles without overheating?

Did you measure the coolant you drained? Put the same amount back in?

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#2106039 - 12/14/10 05:39 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
morris Offline


Registered: 08/24/08
Posts: 3681
Loc: ks, wichita
i have posted this before. but here is the short version. drill a 1/8 inch hole in the stat. recommended by chrysler engineers.

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#2106142 - 12/14/10 06:43 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
sciphi Offline


Registered: 03/24/07
Posts: 8597
Loc: Upstate NY
http://www.pontiacbonnevilleclub.com/forum/viewtopic.php?f=53&t=159

For the GM 3800 V6. It works. Used it 3x on my Buick so far.
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#2106308 - 12/14/10 09:14 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: morris]
edwardh1 Offline


Registered: 01/17/03
Posts: 1682
Loc: Coastal South Carolina
agree. many oem foreign fiters have a hole on top.

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#2106383 - 12/14/10 10:58 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
dwendt44 Offline


Registered: 05/17/06
Posts: 3571
Loc: Central Wisconsin
If you had an air pocket in the engine, the temperature would be higher than normal. You have a bad thermostat.
Yes to drilling the small hole, be sure the place you drill it isn't covered by the gasket or metal housing/manifold.
Find a good brand, usually OEM are 'better'; as in fewer bad in the box ones.
There's a thread here about just that.
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#2106385 - 12/14/10 11:00 PM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
Merkava_4 Offline


Registered: 01/30/07
Posts: 9591
Loc: Clovis, CA
If you look at the reservoir, it's vented; there's really no need the loosen the radiator cap. On mine, I just let the engine idle and get up to 220F. At that temperature, all the trapped air will start belching into the reservoir. As the air comes out, your coolant level will drop down. Keep adding coolant as the level drops below the hot line until all the air is out.

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#2106703 - 12/15/10 11:08 AM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: Trav]
demarpaint Offline


Registered: 07/03/05
Posts: 21563
Loc: NY
Originally Posted By: Trav
I have been reading about these things failing in the open position.If bleeding it brings no improvement its a good chance its failed.Buy an OEM unit from the local GM dealer!


+1 Eventually the air will escape and the coolant level will drop. If the thermostat has been in a while there is a good possibility it is NG. I learned over the years the hard way and always buy OEM when it comes to thermostats. Be certain there is no air in the system, if you are sure there is no air in the system then get an OEM thermostat and install and properly bleed it.
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#2108680 - 12/17/10 09:15 AM Re: Procedure to bleed air from thermostat on 3.8L GM [Re: BLJ]
edwardh1 Offline


Registered: 01/17/03
Posts: 1682
Loc: Coastal South Carolina
Isuzu thermostat had a hole in it, and arrow to tell you the hole went up, and a wiggle piece of metal, like a rivet , loose in the hole to move and keep the hole open.
Great Japanese engineering.
over the counter replacement had none of these things.

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