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Discussion Starter #1
I have a problem with my 01 Jetta. The heater works fine until I stop. Nice warm air blows from all positions until I stop. Then it blows cold air only. Once I take off again, the warm air comes back. Any ideas? Coolant level is good....I think.
 

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Cooling system wasn't properly filled. There's a huge air pocket in your heater core so you only get heat when the coolant sloshes back against the heat exhange for the climate control.
 

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Discussion Starter #3
I haven't had it flushed or changed. It only happens when I stop and the rpm's drop.
 

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What... Why would the radiator have anything to do with the heat on the inside of the car.
Nice initiative but kindly read the post. :p

Yep. Clogged or air. Only 2 things it could be.
Heater cores are quite the job on these cars, requires removing the entire dash and dash supports down to the frame.

Here's to give you an idea

 

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hold on before he goes ripping out his dash lets make sure that he has flow people... make sure that the water pump is actually pressurizing the system properly if not the water pump might be the culprit... ive done countless water pumps on these cars but only 2-3 heater cores.
 

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Discussion Starter #7
Ok. Here is some more info for you...

Car has 150K miles. Water pump changed with timing belt around 92K.

When I'm driving down the road, the heater works fine. When I stop, the air blowing out of the vents becomes cold. Once I take off, the heat returns quickly

Thoughts??
 

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T check the water pump, Remove the thermostat, reach your fingers in and check the water pump impeller.

If the water pump was replaced with a plastic impeller water pump, your are near the mileage where it could have cracked, thus causing your heating issues.
 

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Does revving the engine keep the air warm? Its sounds like a thermostat/waterpump issue.
 

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Discussion Starter #12
Does revving the engine keep the air warm? Its sounds like a thermostat/waterpump issue.
Revving keeps the air warm. I pulled the small return hose off the coolant jug and put it into an empty jug. When I rev the engine, coolant comes out the hose. When I let off, it stops. At first I thought water pump, but now I am not sure. Yesterday morning the temperature didn't reach 190, but it did later I the day.
 

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That could be just because the coolant for the heater core comes straight out of the block. The hotter that coolant is (from a revving engine) the more heat is transferred to the heater-core.

Termostat is cheap, replace it. Since your car isn't making operating temp easily that could very well be the issue.
If it was the waterpump your car should be overheating... I don't think anyone has ever had a lack of heat(at the temp sensor on the block) from a blown water pump.

After the t-stat, if you still don't have hot air then there are two coolant lines behind your block that go to the heater core. With those lines you can check for flow as brian said. You can just get a funnel, some hose and some distilled water. Pour water into the funnel and watch it go down. If it 's barely going in/out its restricted quite a bit and you might need a new one.

Make sure you have the heat control on full heat when you fill and drain coolant to open up the flow to the heater core. Also when testing flow to the heater core.
 

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I am going to let P Diddy answer this one. Diddy what do you have to say? T stat. T stat. T stat. Sorry ever since I saw Jamie fox's impression of P Diddy every time I hear someone say tstat it makes me laugh. Seriously, if you are not making operating temp your thermostat is stuck open or at least not closing all the way. My bet as it gets colder you will notice it more. What you will also notice is that your heat will get worse. Air in the heater core you should be able to hear. It would sound.... Well like air in your heater core. And your post would be worded something like "I think I have a raccoon trapped in my dash. Oh and by the way my heat doesn't work" the only other thing would be poor circulation. I would agree that this could also be likely. Start with the tstat though. And buy the OEM one. Don't make the same mistake I did and buy stant. Good luck.
 

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While your in there changing the thermostat, reach in and check the water pump impeller. You should not have any free play and you shouldn't be able to spin it.. Feel for any broken pieces of the impeller.

Good luck.
 
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