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I have an odd but continuing problem with my 2006 Buick van. (3.9L) It's -6 degrees here this morning. I started it up and let it run for almost half an hour before leaving. When I got in the temp gauge was at normal but all I had was cold air from the vents... until I started driving. As soon as the car was moving (or rpms up) I had all the warm air I wanted. This has been an issue with this car (bought it used three years ago) and it does the same thing with the A/C in summer. Everything works fine but you lose heat or cooling at idle. I've had it in to the dealer twice and all they do is back flush the cooling system but no lasting improvement. Any ideas, recommendations?
 

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Or maybe it's just your radiator being low on coolant.

If your radiator is low, it will blow cold air out while you aren't moving, but may work when you get underway.

If that is it, it's an easy fix.

Good Luck!

Hauxfan!
 

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My stepson just had the same problem on his van, a 3.9. The radiator has to be full right to the top on that motor. He said he only added 2 cups of coolant to fix it. Bill
 

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It could be low on coolant, I am in the process of changing an engine in a Mustang, and as I was scanning the Helms manual they pointed out there is a plug on the top of the thermostat bypass line that has to be bled or it wouldn't heat properly, not a thing about it in the owners manual

Another possibility is at idle you have the strongest vacuum maybe it is pulling a damper too far, or it might be plumbed wrong. A lot of vehicles use vacuum to control the heating and cooling
 

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Flush the heater core. The anti-freeze GM used turns to mud in the heater core I think it's called Dex-Cool, it's junk. Flush the heater core and you will have heat.
 

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If it is not low on anti-freeze and not plugged up, I would bet you have a vacuum hose issue that is letting the vent door stay open until the motor revs up or there is a shutoff valve in your heater hose that is vacuum or electric operated that prevents water from getting to the heater core. Some vehicles do that when the air conditioner is on so the air conditioner will work better.
 

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Revving the engine decreases manifold vacuum but it does increase coolant circulation. My money goes with the low coolant and clogged heater core guys.

I don't recall the underhood layout of the old GM minivans but GM built many models with parts of the cooling system that were higher than the radiator filer neck, resulting in an air pocket when refilling the cooling system. GM's service procedure was to elevate the front of the vehicle until the filler neck IS the highest point in the system.

And DexCool is junk. The freezing protection qualities of coolant never wears out but the rust inhibitors and coolant pump lubricants do, thus the need to change it periodically. In order to give DexCool a longer service interval, the additive package in it was beefed up but it turned to jelly in time and clogged heater cores. We back-flushed the systems with chemicals and refilled the systems with good old green coolant. Owners were advised to go back to the 24-month coolant replacement interval required for green coolant.

Ed
 

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Low coolant. You may also have some air in there.

Park it on some sort of slope, front of truck facing up the slope. Put a bunch or rags around the radiator opening. take off the cap after its cool enough to do so. Start the truck and let it "burp" itself. You will see a few nice air bubbles come out.

be warned you will lose some coolant in the process to be kid to the environment.

Refill to the top and you should be good to go.

Also... if you park with on a downgrade when its cold out, you may not get heat until you start moving, even if you warm the engine up.

My guess is you don;t have enough coolant OR you need to burp it.
 

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I believe there is actually a bleeder valve near the thermostat on that one, if so crack it while its running and make sure no air, next on the list would be waterpump,, you,d be surprised what that crap dexcool does to the fins.... either way not a big $ fix...but i would bet waterpump.....
 

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My GMC truck was the same way, I flushed the heater core and instant heat. Easy way to check. Get the vehicle to operating temp, feel the two hoses to the heater core, if they are cooler or colder than the radiator hoses your heater core needs flushed.
 

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Just spoke with my mechanic he said it could be one of four things.
1) low coolant
2) blend door not opening
3) heater core stopped up
4) cracked head gasket.
He sai check the fluid level first, if that's good check the hoses like I stated above, the blend door runs off of a motor or vacuum, if that's not it a pressure test at a mechanic will tell you about the gaskets. Hope this helps. Ty in Ky
 

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1. Low coolant possible but need to see where its leaking if thats the case
2. If it was a blend door reving the engine up wouldnt make any difference as it has a motor and not actuated by vacuum.
3. Plugged heater core is possibility but not common on gm vans.
4. Doubt cracked head gasket as you would see higher temps after running awhile, and losing antifreeze pretty regular as well as running issues.

Waterpump needs to push the antifreeze through cooling system, if fins deteriorate it wont do it unless you increase rpm....gms are notorius for that in your motor dexcool eats the aluminum fins.... check the waterpump...
 

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Had the same problem with a 2007 Uplander 3.9. Was close to the 100,000 mile service so took it in for a flush and new anti-freeze, noting the no heat at low RPM. Dealership also replaced the thermo at the same time and all has been fine past 3 months. However, I didn't ask but wondered why the gauge alwasys appeared normal operating temp but had the low/no heat fluctuations.
 

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The BIG thing here is Yakimiman says , same in summer with AC. None of the above would address this ? Does it have dual comfort and rear system, if so and the air thing is also acting up , then I would suspect temp door motor trouble. A real pain. Need a scan tool with bidirectional capabilities. Kirk
 

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May have a heater control valve stuck shut. My bet is plugged heater. Remove both hoses and use compressed air. Blow gun shoot air in one hose and see what comes out the other side. Might be a quick fix for winter. Motordoc
 
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